If the store owner got one of those systems that are basically a kit, you really can't screw it up. It's a good way to get your feet wet with the basics. Get a coax and power to each camera (or Cat5e)... that's just wiring. Hook up the switcher, monitor, and the DVR... just plug and play.
Some of these systems can get rather complex. I'm certified on the Phillips (now Bosch) gear, for what it's worth.