Am I understanding hashing correctly?

Question

Hashing

The hash code is obtained after the data arrays go through iterations of the hash functions. Unfortunately, sites write about the hash very briefly, so I have questions:
1) Can I set the length of the hash code myself or is it determined by the hash function and the volume of the data array?
2) Can the hash code be converted back into an array of data? I read that sites themselves do not know user passwords, because they store them in the form of a hash code, it turns out that it is impossible to convert the hash back and read it, or do they not do it out of principle?

Answer 1

1) the hash length is determined by the function. at least for one character, at least for a terabyte, the hash length will be the same.
2) hash is an irreversible transformation.