I’m assuming you got tickets. If so, there was a flyer in the envelope with the tickets that describes the various options. They don’t recommend driving because of the traffic. In addition, the parking fee is steep ($25). There are buses from Port Authority and NJ Transit trains to Secaucus with a connecting train to the stadium.
Of course, this is assuming that you’re coming from Manhattan or someplace from which Manhattan is reasonable to get to. It would help if you told us where you’re coming from.