If you're wanting to make holes for setting snaps, you have the option of using one of the following:
The hole cutting dies cut out a clean circle, like a paper hole punch. In many cases, particularly with vinyl or non-fraying fabric, this open circle makes it easier to slip the stem of the snap or rivet through. Because these dies cut like blades, they will wear down faster than the awl piercing dies and will need to be replaced more frequently, especially the bottom punch die.
The awl piercing dies simply poke a hole, like an earring. It does not leave a clean-cut circle. If your material is very thick/dense, like webbing, it may be easier to use the awl dies since the cutting dies may not be able to cut through. Fabrics that fray may also benefit from a simple piercing rather than cutting to avoid unraveling.
The hand awl works similarly to the awl dies, except you hold it in your hand. This would be ok with thin fabric but may be tiring with thicker/denser materials.