In Judeo-Christian tradition, these two were the first human beings on earth. They lived in a perfect place called the Garden of Eden, where they could eat anything they wanted. Well... almost anything. God told them very specifically not to eat from the Tree of Knowledge of Good and Evil.
All it took was a little convincing from a snake (who some say was Satan in disguise) and Eve was munching on some forbidden fruit and slicing some up for Adam as well. This little incident is often called "the Fall of Man," because it was when Christians believe we fell from the grace of God. As punishment for their crime, Adam and Eve were banished from the Garden of Eden, and all humanity has suffered ever since. (Wow, thanks a lot, Adam and Eve.)