Here's an awl I made today from a small flat-headed screw driver that had long since lost the handle.
I always keep old screwdrivers that are beat up and not really nice looking to be used to make other tools, such as this awl.

The handle is made from a piece of a chair leg that I had to whittle down so it could fit into my hand nicer, the
ferrule is made from copper pipe.

This awl is used right after you've laid out prick marks from your pricking wheel/stich spacing wheel/etc. has been run across the workpiece.

You simply jab this tool into the mark you've made and leave a rhombus shaped hole.

The same thing can be done with a pricking iron, which is a sort of chisel that resembles a fork. Pricking irons can have many points and leave different sized holes and spacing depending on the project.

After you jab this in and leave holes, you can widen them by using a round awl when the leather is wet to make the actual stitching a bit easier.