however, i know nothing about self hosting. My knowledge is absolutely zero […] I dont understand nothing

This is going to be a problem, unfortunately. You’ll need to define your use case first:

• How much music do you want to have access to? Hundreds, thousands, millions of files? How large is your collection?
• Do you have downloaded copies of all the music you want to listen to? Are they all in one place, well organized and tagged? If you just have downloads in the Spotify app, you won’t be able to use those files, you don’t actually own that music. You’ll need DRM-free audio files.
• Where and how do you want to be able to access them? Just from one device like your phone? Many devices? Is having access at home good enough, or do you want to be able to access your collection while you’re away from home?
• Will you be the only user?
• What kind of budget do you have to work with?

An old PC might be enough to act as a server, but there’s more involved and the answer to what you need depends on what exactly you want to do. You will not be able to build a personal version of Spotify with just an old PC, for instance.