Some helpful links to get you started
Above all comb through the late Sheldon Brown’s articles on everything.
New bike? Buy exactly what you want from a friendly local bike shop (walk out if they’re pushy or not friendly) or nail down your size and buy one online from any number of sources. You can get something decent in the $200-$400 range from BikesDirect, Critical Cycles, Public Bikes, Pure Fix–There are far too many to name. One of our mechanics can help you assemble it. If you do it yourself, please don’t force the pedals into the wrong side.