I am a web developer and have enough background in this field and as I know SHA-256 is a one-way algorithm that cannot be decrypted. Then what actually is mining and why it requires such huge resources?
The purpose is to hash the new blockheader. That takes only a few microseconds, but all hashes are not good. The hash result has to meet certain criteria. If you hash again the same block, you obviously get the same hash, but there is a number in the block, called a nonce, that means nothing but is included just so you can change it, and try again.
The criterium for the hash is that it has a certain number of leading zeroes.