It is so important to be certain of your salvation so this is really the best question you could ask.
A christian is a person who relies on Jesus to save them and who follows Jesus as Lord of his life.
The Bible says
"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." (John 3:16)
We are sinners in the eyes of God and because God is just, he punishes us for our sins. The punishment is the condemnation to an eternity without God (this is what hell is).
God knows that there is no way we can save ourselves, because we cannot help but sin and can never reach God’s perfect standards. But because God loves us so much, he gives us Jesus.
Jesus died for us so we can be forgiven by God. By dying on the cross, Jesus took the punishment that we deserved, so giving us eternal life. Eternal life means being with God for eternity (this is what heaven is).
But God also raised Jesus up from the dead, and made him the Lord / master of everything in heaven and on earth. So to believe in Jesus, we also have to treat him as the Lord / master of the universe, including our own lives. We need to follow Jesus in everything we do if we say we believe in him.
So if you admit that you are a sinner needing Jesus, and you rely on Jesus’ death to save you from punishment of your sins, and you are willing to follow Jesus as the Lord of your life, then you are a christian! If you believe these things, then you are a christian regardless of whether you have been baptised, whether your family is christian or which church you go to.
However to be a christian does mean that you need to believe the Bible, because it is from the Bible that we learn about the salvation offered by Jesus, and the Bible is also the way we learn about how to follow Jesus.
The Bible is indeed a very valuable book, because it is the only way God has promised to speak to mankind. The best way to find out if the Bible is true is to read it for yourself. I would start with one of the gospels (the books of Matthew, Mark, Luke or John.) It is also helpful to be part of a church that places an emphasis on teaching the Bible, where the sermon explains passages from the Bible week by week, and where members are committed to study the Bible seriously together in small groups.
The following link has a web site which runs through the christian belief in a short and clear presentation. Why don’t you have a look at it now and make sure you are in a right relationship with God?
You could also look at God Makes Sense. And of course if you have any other questions please feel free to come back and ask.