From midtown, you can walk or take public transportation to an amazing array of classes, attractions and restaurants. Avenue numbers get higher as you go West. Elaborate maps are sold in bookstores, or you can ask for a transit map at any subway station. Most stations are still not equipped to process this dubious innovation and most natives still prefer tokens. One token lets you ride as long as you like and you don't have to pay to transfer, nor to take the Grand Central shuttle across town or change to another line.
Trains run every few minutes.
Be sure you know whether you need a local or an express, and do step on and off quickly, as the doors close fast. During rush hour, trains are always jammed to standing room capacity, but the rides are never very long and most trains are air-conditioned. Just look at your shoes or keep talking to your friend. On the other hand, if you encounter itinerant musicians or hoofers with a portable floor in a subway station, go ahead and put a little something in the hat or the guitar case. These folks are usually very good and most have permits for designated spots.