You can use the bow without there being any wands loaded in it but you won't get any flares from it either. Most wand bows will only take one kind of wand but there are some out there that have been unlocked to take multiple types. Wands hold charges and that is what gets used up when you use a wand bow, each time you fire it takes one charge from a loaded wand. You also lose a high percentage of arrows using one of these bows, there is a 50% change your arrow is destroyed out right from the flare then the usual chance to lose the arrow. I forget how many charges worth of wands you can put in one of these, 80 or 100 I think, but I could be wrong about that.