I've never seen a throwing knife with a moveable weight before. It's obviously to change the balance of the knife to your preference, but most throwing knives are set up 50/50, meaning the balance point is in the exact middle of the knife. If I were you I'd take the weights off and use as is.
There are two ways to throw:
1. Holding the handle.
2. Holding the blade.
What you're trying to accomplish here is a controlled number of turns before striking the target. If you hold it by the blade, you want 1/2 turn or 1-1/2 turns and so on. If you hold it by the handle, you want 1 turn or 2 turns and so on.
Try this. Get about 6 feet from the target, hold it by the blade to where you have about 2 inches of blade in your hand and throw it overhand. Observe how many turns it makes before striking the target.
If it hits the target before it has made 1/2 turn, back up 1 foot or so and try again. If it makes more than 1/2 turn at this distance, you're snapping your wrist too much.
That will get you started and as you get to where you can stick them all the time in a 3 or 4 inch bullseye, back up.
If you're throwing by the blade, triple the distance you're standing from the target and it should be just about right.
In time you'll be able to do it from all kinds of distances by changing how much of the blade you have in your hand when you throw.
My brother and I used to play darts all the time with throwing knives when we were growing up.
I still do it in my garage or backyard from time to time. I use Hibben throwing knives, though.
Ka6otm