What does Unity teach about sin and salvation, heaven and hell?
Sin is our separation from God in consciousness, caused by our belief in the "devil" or a power other than God, the good. This belief leads to our unwise use of our God-given powers and abilities. Salvation is now--not something that occurs after death. It happens whenever we turn our thoughts (repent) from fear, anxiety, worry, and doubt, to thoughts of love, harmony, joy, and peace. The "fall" takes place in consciousness whenever we fall into negative habits of thinking.
Heaven and hell are states of consciousness, not geographical locations. We make our own heaven or hell here and now by our thoughts, words, and deeds.