I'm sometimes seeing people posting screenshots of the game, and i'm wondering how they get those pictures off of the game. could someone please tell me?

Well...I can tell you how to TAKE a screenshot, as far as posting a screenshot, I have no idea.

To take a screenshot, just hit the 'printscreen' key on your keyboard, open up your 'paint' program (located under Start/Accessories/etc.), and then hit Control+V.
Then click File/Save As and name your picture whatever you want (make sure to save it as '.bmp' under file type).

You should crop it with a image editor then you can post it if you have it on a server and a URL to it.