1.) Ask Jesus to come into your life,
2.) Just sincerely ask Jesus' forgiveness for your sins. (All people are sinners, and nobody is better than anyone else. All people are equal. However, Christians have been wiped clean by the HOLY blood of Christ and are therefore sinless and blameless in the eyes of God.)
3.)Admit that you believe Jesus is the Son of God and that He came to earth and died for your sins of His own free will. (IE: He didn't have to die for you, but he CHOSE to because His love for you lasts FOREVER!!!!)
4.) Do your best to live a life according to the Bible. This doesn't mean that if you accidentally stumble every now and then that you are doomed to an eternity in hell; instead, it means that God will forgive ANYTHING that you have done in the past, present or future!! It doesn't matter if you've raped a girl, killed an senior citizen, etc... GOD WILL FORGIVE YOU!! I GUARANTEE IT!!!! If you dont believe me, try the steps above, and see if you dont immediately feel the peace and love of God descending upon you and covering your entire body!!! TEST ME!! (You have to be sincere when you ask His forgiveness though, or nothing will happen. God is not one to be mocked.)
GOD: That's easy. Christianity of course!
There are many different denominations of Christianity, and it is incredibly hard to estimate how many Christians there are in the United States because there is no common belief on what defines a Christian. The most liberal view of everyone who says they are a Christian being a Christian would place the figure around 75%, whereas the considerably more conservative belief that anyone outside your own denomination is not a Christian can place the figure as low as 0.1%.
Denominations sprout from the original idea of Christianity because some phrases from the bible contridict each other, and thus to harmonise this people say phrase A is literal whereas phrase B is symbolic. However, one group might say A is symbolic, but another might say B is symbolic. Thus, there are now hundreds of different denominations preaching slightly different versions of effectively the same source material.
Unfortunately, as Christianity is the 'big' religion of the Western World, it gets a lot of negative press. However, like all groups, Christianity has the best and worst among their number. The Christians who get the most press are the ones who give the stereotypical image of never doing anything wrong, and sitting on streets shout 'REPENT OR GO TO HELL', or something similarly pleasant.
However, many Christians - most, in fact - are decent people who just want the right to practice their own religion, like everyone else (or the right to NOT practice a religion, in the case of some).