Pre approval letter for a car

So I got a pre approval letter for a car. Is it legit? This would be my first car and first purchase. What all would I need? I don’t have my license yet but I think I still have an active permit and planning on getting my license tmr if I can. I don’t have any money for a down payment and I also don’t have insurance yet. Is it still possible for me to get a car used or new? Or am I just waisting my time? Answer ASAP please