When was the concept of Heaven or Hell first introduced in the Bible? Did Adam and Eve know that faith was required to enter Heaven?
The first reference to death and the way to eternal life is found in Genesis 3:
Gen. 3:22 Then the LORD God said, “Behold, the man has become like one of Us, knowing good and evil; and now, he might stretch out his hand, and take also from the tree of life, and eat, and live forever” —
Gen. 3:23 therefore the LORD God sent him out from the garden of Eden, to cultivate the ground from which he was taken.
Gen. 3:24 So He drove the man out; and at the east of the garden of Eden He stationed the cherubim and the flaming sword which turned every direction to guard the way to the tree of life.
The Lord alludes to living forever as He references the tree of life. Later, God revealed more and more details of life after death to mankind progressively over centuries of time, but that process isn't necessarily recorded in Scripture. For example, Abel and Cain knew to sacrifice to God as seen in Genesis 4, but the moment they learned this requirement isn't recorded in Scripture. More than likely, they learned it from their parents, who experienced the first sacrificial act in Genesis 3:21.