I was thinking about buying one as a secondary tablet, but I'm not really sure how they work?? I've watched a few videos and checked out some reviews but I can't seem to find the one answer I'm looking for.

Can you use them without being directly attached to the computer? I mainly want one so I can sit in my bed and doodle at night during the week. I only get the chance to draw on Saturday and that really bums me out. Or if not is there a tablet that has this kind of capability?? It doesn't have to be wacom, I'm honestly willing to try anything at this point.