They attach to the existing wll studs with #10 x 2 1/2" wood screws. I used 2x 8 lumber of the heavy stuff and 3/4 t&g OSB for the other shelves and work bench top. They are simple and FAST to install and or alter for height changes.
They are sold at Home Depot but for some reason not in the area they sell shelving but over in lumber area. They are "FAST-MOUNT" , the 14" shelf brackets are rated for 300lbs, the bar code is 77355 01031 & they are made in the USA ! Sizes range from 6' to 24" (I bought 14" f/shelves and 24" f/work bench.
I see alot of people building shelving and benches in their garages. When I built mine I found some 300lb shelf brackets that are adjustable (1.5" each step up or down) and they work great for shelving & benches. The brackets keep your floor clear of drop leg suports for all the above. Spaced at 6 feet apart (mine) they hold easily thousands of pounds of junk (precious treasures lol) .
I drive a base model 4-wheel drive extended cab, manual transmission, 4 cylinder SR5 Tacoma. Mileage is pretty good and rides pretty well. I love the looks of it. When I bought it I only needed to haul a lawn mower or two and other yard items. It won't pull much more than that if there are any hills to speak of. Still, good for what I needed at the time.