There are primarily two types of garden dibblers: those for planting seeds, and those for planting bulbs. Bulb dibblers are typically longer with a fatter body and pointed to create a large hole. They generally have a flat point to create a firm contact point for the bottom of the bulb, and have lines marked at one-inch intervals for reference.

Seed dibblers on the other hand are typically skinny and pointy, to create a small hole for starting seeds.  Some dibblers will have half-inch markings in addition to one-inch increments.

You can also place the dibbler flat on the ground and use the one-inch marking to ensure you place your seeds/plants the correct distance from each other.