Driveway sealing is best repeated every couple of years, with the exact frequency depending on how much wear and tear your driveway suffers. If you live in the northeast, or anyplace where rock salt is used on your driveway, it will need to be repeated more often. Cut down maintenance by switching from sodium-based rock salt, which is very corrosive, to calcium chloride ice melt pellets, which are much kinder to your driveway surface.
Driveway sealing itself is pretty straightforward. You begin by patching and filling cracks, and then apply a thin coat of asphalt sealer. I recommend Quiktete Concrete Patching Compound. And whatever you do, avoid putting new concrete on top of old, damaged concrete. It doesn't work. The old concrete doesn't have the necessary adhesive qualities, and as soon as the patched job gets wet or freezes, that new layer comes right off.