Remember, there are no stupid questions. Just stupid people.
JK. Backspacing is simply the term used to describe how far the center of the wheel is from the inside lip. For instance, if you had 0 backspacing, the tire would stick out dramatically. Wheels have various backspacing, so if you pick the correct one, the tire will not rub any suspension or steering components. Or, if you care at all, not stick out too far.