What is the purpose of the SHA-256 hash?
The purpose of the SHA-256 hash (and of any hash function) is to generate a summary. To understand this in a simple and more detailed way, do not miss the chapter dedicated to explaining the functions hash.
In Bitcoin, SHA-256 is used for mining process (creation of bitcoins), but also in the process of generating bitcoin addresses. This is so due to the high level of security it offers.
Within the blockchain network all the nodes they would have a copy of the 64-character hash representing the information that represents, for example, an entire block. Once that information is validated by the network (or what is the same, has already been registered in the chain) any manipulation of that information trying to modify some character of the validated hash, would be detected immediately and would be discarded.
To increase the technical information about this cryptographic hash function, we recommend you download and read the paper in Spanish "Cryptography: SHA-256 function" de Javier Domínguez Gómez, Spanish software engineer and hacktivist at Free Software Foundation y Electronic Frontier Foundation.
If you want to test you can access this SHA-256 based password generation page, by clicking here.