I'm a noob don't hate me but what is bump? Pm? Is it a bad thing?

"Bump" is when a trade thread moves to the top of the trade forum because it is the most recent. It becomes the most recent because someone has made a new post in that thread.
Usually it's the original poster, the guy who started the thread. He'll make a post that just says "Bump!" because he doesn't want his thread to go stale and be lost at the bottom of the pile.
I think you are only allowed to do it once in a while, for specifics on that go find the trade forum Rules thread.

"PM" is short for "private message". If I say "i have a trade offer, so I will pm you." it means I'm sending you a private message, and I'm letting you know in public on your trade thread in order to Bump it up, just to be nice to you - I'm keeping your trade thread fresh.

Thanks that's all good to know.