Remove the bracket from the runners and leave them in the cabinet. Then mark and pre-drill the runner hole closest to the edge of the cabinet. Repeat this process for the other runner, making sure you space it out according to the measurements in your instructions.
Screw down the first hole and then mark and pre-drill and screw down the back hole. Use your tape measure to keep the runner straight. Use your spirit level to check that it's straight. Then screw into the rest of your holes. Repeat this process for the other runner.
Slide the bracket onto the runners. Turn the cabinet back upright and slide your baskets onto the bracket. Then check that the unit slides in and out properly and you're done.