Is your floor level? Garage probably not. Those that are well done have a slope. Level up from the high spot and repeat. Mine is an inch and a half with no backer. Backer might not be a bad idea. Guess I just never saw a reason.
Assuming you already have a drill get yourself a drill guide. This will allow for a straight hole or an angled one. Also use a Forstner drill bit of the right size. It will cut a nice consistent hole. Don't use a paddle bit, they tend to wobble and should only be used for rough cutting. On a peg board, 1" deep might be good for a hardwood but if you are using ply or 2 x 4s maybe a bit deeper. I'm not sure as I have never made one, but I was a custom woodworker for 8 years. Do a bit of research for the depth. Every peg board I have used does have a set depth which can be achieved with a backboard or just drilling to a particular depth. The drill guides usually have a set collar on one leg.