If you want to use the trains: From Newark Airport take the Airtrain to connect to the NJ Transit (train). Take this to Newark Penn Station (one stop in the direction towards NYC). From there you can connect to the Path train to Hoboken. If you post the day/time of arrival we can guide you better. Total price for this is around $9-10.

There are also bus routes as jackal pointed out that are cheaper, and may be more convenient depending on where your destination in Hoboken is.

The google transit tip is a good one!