Has is function that converts an input data into an encrypted output. It cannot be used to 'reverse' the input from the hashed output like a only way flow of water in rivers. 

One of the key role is data structures in computing systems like authenticating information and checking of massive. 'If this hash is less than or equal the target hash, then it is accepted as the solution, the miner is given the reward, and the block is added to the block chain' Investopedia. 

There are three common features of hash function in the Cryptographic 

1. Collision-free

2. Hidden

3. Puzzle-Friendly