On Mount Sainai, God gave Moses two stone tablets with the 10 rules by which everyone should live by. He also explained each one in detail telling him how and why everyone should follow these commandments to live a moral life. The first 3 commandments tell how we should Love God, and of coarse the last 7 seven tell you how to Love thy Neighbor.
The "10 Commandments" are also often known as the "Decalouge", which literally means "ten words". The 10 Commandments is also a summary of the 613 laws to live by in the Old Testament (365 negative refer to days, and the other 248 positive laws refer to the joints of the human body). The church also believes that if someone breaks single commandment, then they're breaking the whole "Law".