They auto drill for you, and when a drill runs out they re-quip one for you as long as there is another drill to be re-equipped. You equip the pet, press D, right click as if you were going to drill something and watch as they do it for you from there. They will Auto loot everything they drill as long as you have space, or as long as you have the item they drill up in your inventory. Most people only want certain items they drill, o they max out the inventory @ 300/300. A good example is Driller Boxes, people leave 300/300 Items and one of those items are Driller Boxes and the rest is nothing that would be drilled up in that area, hence you will only pick up the boxes.
I hope my explanation has helped you lmao.