What is the difference in denominations and how do you know who is right? The understanding that I get from the Bible is that we should all be followers of our Lord Christ Jesus. So why do we add our own opinions of what we get from scriptures and make it a denomination totally separate from another group who claims to be following Christ also? Plus a non denominational church is like a denomination in its self.

Denominations are definitely with us and will certainly be with us until the coming of Christ. Many people see denominations as an evil in the world. Most who hate the idea of denominations go to the prayer of Christ in the Garden of Gethsemane. In John 17:11And now I am no more in the world, but these are in the world, and I come to thee. Holy Father, keep through thine own name those whom thou hast given me, that they may be one, as we are.
See All..., He prayed, "And now I am no more in the world, but these are in the world, and I come to thee. Holy Father, keep through thine own name those whom thou hast given me, that they may be one, as we are." Therefore, if it was the desire and prayer of Jesus that His followers be one, then the divisions brought on by denominations must be evil. This conviction has caused many to come up with ways to bring about this oneness. Unfortunately, human devices that seek to obtain God's almost always fail. Here are the main contenders that seek to bring about this oneness.

1. One approach is to start a group and then deny that it is a denomination. This is the practice of the non-denominational movement, the Churches of Christ, and others. But this approach ends up being no more than a hoax. The verb, to denominate, means to give a name to something in order to distinguish it from other similar things. Therefore, as soon as a group has a name that identifies them as a group that is different in some ways from other groups, they have become a denomination. To deny this is to deny the obvious.
2. Another approach is to attempt a joining of denominations in an ecumenical movement. This has been the goal of the liberal churches for decades. In fact, I think they will eventually succeed. The bad news is that, when they do, what they have will not be the true body of Christ but rather the church of the antichrist. For the ecumenical movement to work, churches have to be convinced that doctrinal beliefs and church practices mean nothing and that nothing is worth dividing over. However, this flies in the face of New Testament teaching. Titus 3:10A man that is an heretick after the first and second admonition reject;
   See All... states, "A man that is an heretick after the first and second admonition reject." We are not to allow heretics in the church. But one church's heretic is another church's orthodox believer.
3. A third approach (similar to the second) is to accept the claim of Roman Catholicism that they are the original and true church and slowly merge back into the fold of the Catholic Church. This is indeed where ecumenicalism will eventually end. But there are those like myself who are convinced that the Roman Catholic church left the truth of God's Holy Word so many centuries ago that it cannot be considered a church today.

I, and many other both like me and quite different from me, cannot accept any of these three choices. I am convinced that the churches cannot and will not be united in any godly way by the efforts of man. In fact, if you think about it, that is not what Jesus prayed. Jesus prayed to the Father that they may be one. This is evidently a work of God and not a work of man. Also, it does not necessarily refer to outward titles or denominational names. Jesus prayed: "Holy Father, keep through thine own name those whom thou hast given me, that they may be one, as we are." Believers are one by the power of the Father in keeping through His name those He has given to the Son. 

I believe that the references in the gospel of John to those given by the Father to the Son refer to the true saints of God who believed in Him before the revelation of Jesus as the Messiah. When Jesus came, the Father gave all who truly believed in Him to the Son. That is, all of the true believers in the Father accepted Jesus as the Messiah when they were introduced to Him. This refers to Jewish believers. But Jesus is praying not for "these alone, but for them also which shall believe on me through their word" (John 17:20Neither pray I for these alone, but for them also which shall believe on me through their word;
See All...). Many of these later believers would be Gentiles. One of the most spectacular shifts in thought that could have been imagined at the time of Jesus was that Jew and Gentile could be made one in Christ, but this is exactly what happened--in part as an answer to the prayer of Christ in John 17. Ephesians 2:11-22 [11] Wherefore remember, that ye being in time past Gentiles in the flesh, who are called Uncircumcision by that which is called the Circumcision in the flesh made by hands; [12] That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world: [13] But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ. [14] For he is our peace, who hath made both one, and hath broken down the middle wall of partition between us; [15] Having abolished in his flesh the enmity, even the law of commandments contained in ordinances; for to make in himself of twain one new man, so making peace; [16] And that he might reconcile both unto God in one body by the cross, having slain the enmity thereby: [17] And came and preached peace to you which were afar off, and to them that were nigh. [18] For through him we both have access by one Spirit unto the Father. [19] Now therefore ye are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God; [20] And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone; [21] In whom all the building fitly framed together groweth unto an holy temple in the Lord: [22] In whom ye also are builded together for an habitation of God through the Spirit.
See All... deals with this oneness in Christ in great detail. Paul said concerning Jesus Christ: "For he is our peace, who hath made both one, and hath broken down the middle wall of partition between us" (Ephesians 2:14For he is our peace, who hath made both one, and hath broken down the middle wall of partition between us;
See All...). The "both" in context are Jew and Gentile. In this, the prayer of Jesus in Gethsemane was truly answered. 

I would take this one more step though. I share a true oneness with other believers in Christ despite denominational names and variations in doctrine. I have worked alongside true believers who went to churches of other denominations. And although we did not agree in every whit and did not change each other's mind on our differences, we still shared a oneness that was not shared with unbelievers. I would also say that those who were lost did not notice so much our differences to each other as they noticed our differences to them. Generally, they tended to see us simply as Christians and the divide they saw was between the believers and the unbelievers. There are many ways in which the prayer of Christ is answered at this time. It will be enough that we have to wait for its final fulfillment through the direct working of the Father. 

So, why are there different denominations? They are there because all men do not see the same thing in the Bible. However, the problem is not with the Bible but with men. Most denominations have a small number of foundational approaches to truth or doctrinal beliefs that they count as the base of truth for believers. These foundational beliefs lead to most of the remainder of their doctrines. For instance, Baptists give an extremely high priority to the authority of the Word of God. However, Baptists also believe very strongly in a dispensational shift from the beginning of the apostolic age to the mature practice of the Christians later in the apostolic age. That is, they see the book of Acts and that time period as a transitional period containing things that were only for the initial offering of the gospel and not for all times. Pentecostals, however, tend to try to go back to the early apostolic times and try to relive that time. Though I think this is wrong, I admit that they are truly trying to be biblical--at least in most cases. 

I may accept that many Pentecostals are truly saved. However, the differences are of such major import that I cannot accept them and they could not accept me in fellowship in one church. One side or the other would have to compromise their heartfelt beliefs. Yet, denominations are not all bad. They allow these differences in belief to be aired, argued, and considered. I am forced to know why I believe what I believe and this is biblical (1 Peter 3:15But sanctify the Lord God in your hearts: and be ready always to give an answer to every man that asketh you a reason of the hope that is in you with meekness and fear:
See All...).

There is yet another benefit of denominations. They force people like you to consider the differences and make a commitment on the basis of what you have concluded. Now I admit that this is not what normally happens. Most churches are trying so hard to remove any semblance of distinctive features that they are almost impossible for the casual observer to see. And most people are drawn to a particular church for totally unbiblical reasons--a friend is there, they like the music, the church is friendly, they have a program for their kids, and so on. 

You have an opportunity to use your initial confusion to ask hard questions and discover God's truth for yourself. What does this church believe? How is it different from the church down the street? What are your biblical reasons for doing what you do? These and other questions can lead to a discovery of God's truth--although I admit that many will be baffled that you would ask such questions. Use the differences to define the truth. Use them to define your personal convictions and beliefs. I would like you to have mine, but I have found that I cannot impress my beliefs and convictions on others. However, I am convinced that an honest and serious pursuit of God's truth will bring almost anyone closer to it than they were before they started. May the Lord guide you as you seek Him and His truth.