Christianity started with the birth of the world by the hands of God. After he created the first man and women and when they sinned he sent them into the real world. In the real world there was lots of sin.
Then the Angel Gabriel visited a woman named Mary and asked her if she would give birth to the Messiah. Nine months later the Virgin Mary gave birth to Jesus Christ on December, 25th starting Anno Domini (A.D.), the Year of our Lord. He led people called his disciples to preach the word of his Father. Ultimately leading to his crucifixion by the Romans at age 32.
That you should pray for forgiveness to God after committing a sin to achieve the goal of going to heaven. Also, to go through a Communion multiple times per year to cleanse your body of sin and to basically be reborn and repealed of all previous sin.
Christmas marks the birth of Jesus on December 25th. Easter marks the resurrection of Jesus three days after Good Friday which is the day that he was crucified.
The Ten Commandments are the rules that God established in the Old Testament. You had to follow these rules in order to go to heaven. Christians read the Holy Bible to receive the Word of God. It was written over a millennium by several different authors and has many different versions.