Welcome... You can find maps all over the INTARDNETS. MTBNJ has a list of ALL major areas to ride. NJ state maps can be gotten trail side (normally only in spring) and on the web site for each park. AND as has been mentioned there are maps stuck to the top of most threads.
However, when it come to riding... do not start alone. Like Brian said, join the beginner rides from this site or post that you are looking for a ride. Safety in numbers and all that jazz.
Have fun and enjoy.
Cheers,
"slow" Joe