Your arrows should match the draw weight of your bow. Get some cheap arrows to start since they'll most likely break as you practice (most of practicing when starting out is trying to not miss the target). Arrows that are too light and they'll fly wonky, too heavy and they'll drop in flight (won't fly as far).
Length is important, you don't want an arrow thats too short. Arrows that are too long aren't too big of a deal, though. We usually advise getting arrows as long as possible so that if the arrow breaks (and that usually happens close to the tip) you can cut the arrow shorter and keep using them.
The big question is what kind of bow are you shooting? Is it wood? Fiberglass? Some form of combination? Is it a longbow/ flatbow? Recurve? They all shoot different, and different types of arrows will fly differently. Best advice for everything concerning starting archery is experiment and find what you like best.
