You must first determine which foot will ride forward, or in front, on the wakeboard. If you don't know, use my article "Which Foot Forward?" to help make your decision.
Wakeboards and binding plates (the plate on which the boot rests) come with multiple pre-drilled holes that allow you to easily change the angle and position of the bindings on the board. The angle at which the binding is placed on the board is referred to as "degrees," just like in geometry.
The width at which the bindings will be apart can be determined by jumping up in the air. However your feet land naturally on the ground will most likely be the width apart at which you'll set your bindings. It is usually shoulder width apart.
Tip: Get in the practice of making sure your bindings are snug and secure before you hit the water. Taking this extra step can help prevent injuries.