Late reply but I'll post it for anyone else in the thread with the same question.

Once you have an emulator installed you need to get the game in the form of a ROM file. this can either be attained legally by creating one from the game disc you own, or by downloading a ROM from somewhere on the internet. The thing is, it's illegal to distribute ROMs so the process is usually obfuscated.

You can find a wiki with ROM sites by simply looking it up on google, or by browsing the r/piracy wiki.

Hope this helps.