How do I play SNES games online on pc?

There are a bunch of sites out there that host SNES and classic Nintendo games. http://www.snesfun.com/ is one example.

Often you'll find that the games shouldn't be hosted on the site because the correct licenses and permissions aren't in order... In this case there's a good chance the site will get closed down eventually.

You can download a emulator for SNES and download game files.

To get games I recommend emuparadise.

http://www.emuparadise.me/