Algorithm

Question

what a “Hash Algorithm” is and what are they used for?

Answer 1

A hash function will take any amount of data and turn it's content into a small "fingerprint", ir "checksum".
For example, no matter whether you put your name (small) into SHA-2 224, or an 80 gigabyte movie (big), it will always give you a result that is 224 bits long.
0xd14a028c2a3a2bc9476102bb288234c415a2b01f828ea62ac5b3e42f
A well designed hash function makes it impossible to tell what went into it, so you can't turn the hash back into the original contents.
Also, if you change just a single bit in the input data, the resulting hash will look completely different.
Common example: You download an 80gb movie off a website. They also provide a hash of the file. Once you have completed the download you can hash it yourself and confirm that they are the same. Then you know the download completed successfully and nobody was messing with your internet connection.
As you can imagine, hashes have many applications in cryptography. In computer science, hashes are used in for example hash maps.