The word genesis means 'beginning' - an appropriate title for the book of the same name. Not only is it the beginning of the Bible, being the first book, it also tells of the beginning of the world and how it was created by God. The Book of Genesis also describes how sin came into the world and how God exercises His judgement, but also His mercy, on mankind.
Genesis 2:1-3
"Thus the heavens and the earth were finished, and all the host of them. And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made. And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made"