INTRODUCTION TO CHRISTIANITY
Christianity is a Semitic religion, which claims to have nearly 2.1 billion adherents all over the world. Christianity owes its name to Jesus Christ (Actual name is Eesa, peace be on him). The Bible is the sacred scripture of the Christians. The current pontiff or head of Christianity is Francis 
The Bible is the sacred scripture of the Christians:
b) The complete Bible, i.e. the Old Testament and the New Testament put together, contains 73 books. However, the Protestant Bible i.e. the King James Version, contains only 66 books as they consider 7 books of the Old Testament to be apocrypha, i.e. of doubtful authority.
Christians believe that there is only one God, whom they call Father as Jesus Christ taught them.
Original sin is an Augustine Christian doctrine that says that everyone is born sinful. In traditional Christian teaching, original sin is the result of Adam and Eve's disobedience to God when they ate a forbidden fruit in the Garden of Eden.
Some Christians believe that human beings can't cure themselves of original sin. The only way they can be saved from its consequences is by the grace of God. The only way people can receive God's grace is by accepting his love and forgiveness, believing that Jesus Christ died on the cross to redeem their sins, and getting baptised. 
Christians believe in the Trinity - that is, in God as Father, Son and Holy Spirit.
These days, the word saint is most commonly used to refer to a Christian who has lived a particularly good and holy life on earth, and with whom miracles are claimed to have been associated after their death.
Prayer is the means by which Christians communicate with their God. 
The pope is the Bishop of Rome, based in the Vatican City, and head of the Roman Catholic Church. Pope comes from the Latin for 'father' (the traditional title for a bishop). The adjective for something relating to the Pope is papal.
Catholics believe that the pope is the successor to Saint Peter whom Jesus appointed as the first head of his church. The current pontiff FRANCIS is the 266th pope and succeeded Pope Benedict XVI in 2013.