Muddy Creek suggests a track saw, but frankly, the Xuron Rail Cutters are soooooo much better, simpler to use, and also safer. (If you've ever snagged yourself on a saw, you'll know what I mean.) I would steer you towards the Kato F3 set, its really the only set in N scale that is all quality components. Get that, a powerpack, and you're on your way. Otherwise, stick with Atlas and Kato locomotives for your first couple of locos, and Atlas or Peco track.
Pay close attention to the couplers on the locomotives that you buy. Basically, there's three types. The old, clunky looking Rapido couplers that don't look anything like real railroads use, "dummy" knuckle couplers that look like real ones, but don't actually open and close, and finally, operating knuckles. Try to stick with operating knuckle couplers only when buying new equipment. With the exception of older stock on the shelves, there is very little quality equipment today being produced with Rapidos for the North American market. (Spectrum Steam and the Atlas Mogul are all I can think of....)
Most important thing: dive in and have fun. With anything that you "build", i.e. track, structures, scenery, just go slow, accept that you'll make mistakes because there's a lot of different skills that come into play with Model railroading, and don't worry that what you're doing isn't ready for the cover of Model Railroader's Great Railroads 2006. Sometimes the fun is in learning to do something, doing it again, and again, then looking back at your first effort and seeing how far you've progressed.
As Nike says, "Just Do It!"