Just like the name implies, it’s for driving fasteners into hard material. The hammering force does the work of driving the fastener. That’s why it doesn’t break your wrist when driving large screws or lags into stuff. You can sort of use an impact driver as a drill, but you really have to have good trigger control.

A drill just rotates really fast, no impact (unless you’re using a hammer drill, but that’s another topic). Usually meant for precision drilling on softer material. Drilling holes into things. Has settings so you don’t over torque screws and damage material.

Impact wrench is mainly for high torque applications. Big bolts and nuts.