Essentially, you have a couple of options! Either Q can wink your character over just before they die, thus keeping them alive if you so desire, or if they've been dead for a while he can grant them a corporeal body, sort of like a solid ghost. That last option carries with it the ability to function just like a normal person in the game, with such things as eating and sleeping, and they can go to worlds and starbases as well, but if they get too far away from the Enterprise they will start to lose tangibility. Unfortunately, that last option means that the deceased can't go home like the live character would, either.

Does that answer your question?