How is ssh fingerprint calculated?

Question

SSH

The first time you try to connect via ssh to the server, a message comes up asking if this is really the fingerprint, confirm.

The question is how it is calculated on my computer for the first time. Yes, it is based on the public key of the server and the unique keys of the server. But, what's stopping someone from trying to fake it? That is, so that when I try to connect, this fingerprint is shown to me, but it would not be a real server?

More precisely, the question is, how is this fingerprint, what is written in my terminal, calculated locally if I only know the public key of the server and do not know the unique keys of the server?

Thank you. I did not find detailed articles or information