Well, the PM stands for personal message, and if you click it over someone's post it will send them a private message from you. Much like an email, with the difference that it won't actually mail it to them, instead they'll just get a little notice about it next time the visit Pet Talk. A forum is the same thing as a board, which are places like these. An online communinty where people can talk and post messages. A thread is what we call each seperate subject, like this whole thing is one thread, and what I'm doing right now is just a post.

Oki, I hope that helps some! I gotta run so I can't respond to your other questions (sorry!), but I'm sure they were will be others around, eager to help