There was a version called Protools Free quite a while back. If you're still running windows 98 or Mac os9 you could be in luck. Any other versions you find will require digidesign or Mbox hardware to run anyway.
I guess you could watch some YouTube tutorials to get a good idea of how it works. The point is though, it's good enough to be used for anything from homegrown VoiceOver booths to Hollywood film scores.
If you want a free trial (and very cheap anyway) alternative you could try Reaper. It's good, buts it's no Protools.
"Audacity" might be worth a look too. Also free. Used to be called "Cool Edit" back in the day.
Here's a handy comparison grid on a respected site: