Mike, the sub-panel referred to is much like your main panel, but usually smaller, and with a smaller ampacity. It makes sense to use a sub-panel if you have to run several circuits that are a fair distance from the main panel, or if you have a limited number of breaker slots available. If you want to go that way, you will need to get a book and do some studying since there are a number of details to be taken into account. (e-mail me if you need a book recomendation). The general purpose receptacles in the garage are usually required to be GFCI protected. GFCI breakers will do the job, but they are very expensive and have a reletivly short life expectance compared to regular breakers. If it were me I'd just make the first outlet of each circuit a GFCI and use normal breakers. If the first outlet is a GFCI, and if subsequent breakers are connected to it's load side, the whole circuit will be protected. PS. When you get around to that compressor, keep in mind that motor circuits are sized differently than regular circuits, for instance, a true 5hp compressor would require a dedicated 35 A. circuit breaker and 8 AWG NM cable.