What pieces of information do you need to unhash a key to find out the original message? I am very new to the hashing world and despite hours of research (AKA Googling) I still don't understand this piece of information. What are the different pieces of information that are needed in order to unhash a SHA-256 key to reveal the original message, besides the original message itself? Or if I am way off base, what information do you need that gets you the closest to unhashing the SHA-256 key?

The closest thing I could find was this question and I would comment a question, but unfortunately, I bear the newbie banner.

If this has been answered, a redirect link or some good reading materials outside of Wikipedia would be great! I am just not sure of how/if I am asking the right questions.
You can't reverse a hash, because hash functions are one-way-functions by design. The best you can do is brute-forcing, meaning you try every input until you get the same hash-value and even then you can't be sure if you have found a hash-collision or the original message.