Pretty much what other posters have been saying: the story of the Fall represents our human capacity to sin and our nature to turn away from God. It’s an allegory and a myth, but a very true one at that. I don’t see any conflict between this and the fact of evolution.
The significance Jesus’ sacrifice and death is a tricky one to comprehend, even if you’re a young earth Creationist who thinks Adam and Eve existed 6,000 years ago. I’ve spent some time reading about different theories as to the atonement, and I still don’t know if I really “get” it yet. However, I have been moving away from substitutionary atonement to the Christus Victor theory, which was held by most Christians for the first millenia or so. Essentially, Jesus submitted himself to the world, allowing the powers and principalities of this earth to mock him, beat him, and kill him, exposing all that is evil, and with his resurrection, Christ conquered the powers that sought to destroy him, defeating death and showing us Christians the way to becoming closer to God.
It’s more complicated than that, but it’s the one that makes most sense to me.