What is a Christian?

A Christian is simply a follower of Christ. Someone who seeks to live there life like Jesus would. Of course we are not God and we all mess up but there is Good News! God, our heavenly Father sent his son Jesus Christ to die on the cross for the forgiveness of our sins (the things we do wrong and outside of God's will). By God's grace we can be forgiven. Grace and mercy is given not because of anything we do. The only thing God asks from us is for us to repent, to ask to be forgiven by saying we are sorry for those wrong things, to turn around and to follow him. 
John 3:16-17 says this, 'For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. For God did not send his Son into the world to condemn the world, but to save the world through him.' 
It is through a personal relationship with Jesus that we can put ourselves right with God and call him our Father. Whilst out earthly father may fall short in many ways our heavenly Father is everything you could possibly want and more. He loves you and wants to spend time with you. Yes, even you, no matter what you have done wrong in the past.  
If you would like to become a Christian then after you have repented and asked forgiveness you simply need to accept Jesus into your heart and for God's Holy Spirit to fill you with his love. There is so much more that could be said here but being a Christian and following Jesus is not about having lots of head knowledge but having heart knowledge. Faith in God is not a head thing rather it is an experience of the heart and putting your trust in him. You may find it helpful to pray this prayer:
Dear Lord Jesus, I know that I am a sinner, and I ask for Your forgiveness. I believe You died for my sins and rose from the dead. I turn from my sins and invite You to come into my heart and life. I want to trust and follow You as my Lord and Savior. Please fill my heart with your Holy Sprit and your love. Amen.
If you have done this please leave a comment so that I can pray for you (I will not post these so please do not worry).