I feel like, given that we've had so much debate over the subject, it would be in the best interest for someone who identifies as a Christian to lay out what they believe, since it hasn't been done yet. Keep in mind that this is a short summary of what I believe, so it may not seem complete, and others may differ in opinion.
1. God created the heavens and the Earth. Basically, everything that exists in the physical was made by God, whether directly or indirectly. He did this to glorify Himself, similar to the way artists show off their works in a gallery, or a Know Your Meme user writes a really clever comment to get karma. Whether he did this in 7 solar days or several hundred million years is, to me, unimportant; what matters is He did so.
2. God created man and gave them the choice of perfection or sin. They chose sin. We've all heard the Adam and Eve story, I assume, so I won't rehash the nitty gritty, but the point is that God created humans and said, "don't eat from the tree of the knowledge of good and evil." Adam and Eve ate from the tree, and thus sinned: not only did they directly disobey God, but they gained awareness of what evil is, which means they had the potential to sin again from that point on. This separated humanity from God, as evil is against God, and a God who is just cannot tolerate that which is against Him. And we're all guilty. We have an awareness of evil, which means we can choose it over God, and we all have. In fact, I gotta be honest, I feel like I'm the worst about it. Anyone who doesn't believe at least has the excuse of that; I talk all the time that I believe it, and I'm still hypocritical and judgemental towards others.
3. God sent His son, Jesus Christ, to take on the punishment our sin required that we may be forgiven through his death. From the get go in Genesis, God lets the world know that he has a plan to solve the issue of their sin. This plan came in the form of Jesus of Nazarene. By Christian beliefs, he was fully God and fully man, which means he could fulfill the need for perfection that God required. However, being perfect wasn't enough. Because he was perfect, he had no debt of his own to pay, and therefore could pay another's debt. "Another" in this case being the entirety of humanity from start to finish. He did so by being crucified on a cross, a Roman execution tool that caused death by wet suffocation, or the lungs filling up with blood and water. Not only that, but the cross was the ultimate humiliation, as passersby could everyone who had rebelled against Rome and failed.
4. Jesus rose again three days later. This is the part where things honestly get wild. Jesus was buried in a tomb by some of his followers after being wrapped in about 50 lbs. of burial gauze. To make sure that his body wasn't stolen, Roman soldiers were posted outside the tomb and a large stone was placed in front of the entrance, as the officials believed people would try to steal his body. And yet, three days later, the stone was rolled away, the soldiers were both rendered unconscious, and Jesus' body had disappeared. This is the most important part of the Christian faith, because if Jesus hadn't rose again, he wouldn't have overcome death, and damnation, which was the whole purpose of his death.
5. We are innocent in God's eyes through Jesus' death. When we believe that all this truly happened, and that God loved/loves/will love us enough to send his son to die and rise again for us, we're provided with salvation in Him and a relationship with Him. And there's nothing that take that away. Doesn't matter what you've done, are doing, will do, in Christ, there's payment for sins.
Hope that clears any issues up, guys.