The Hunterdon Militia, as it was sometimes called, was a very decentralized militia in New Jersey, consisting of small bands of volunteer rebels working outside of Washington's army, in groups as small as three up to whole units of two hundred or more.
They relied on guerrilla tactics, attacking Hessian and British patrols only when they were sure they could win, hiding weapons in easy to reach places and collecting and using them only when an easy target presented itself.
While these units didn't make a huge tactical difference in the battles for New Jersey, what they did do was tie down fairly large numbers of Hessian troops. Colonel Rall, the Hessian commander, often had to send 50 or 100 soldiers simply to escort a dispatch outside the cities of Trenton or Princeton, and patrols a short distance outside of town were vulnerable to sniping and ambushes. These troops were then not available for the defense of Trenton, while Washington's army could have relative freedom of movement, and the Hessian/British intelligence on his whereabouts was limited.
This made it much easier for Washington to take the initiative and achieve military surprise, the key to almost all of his New Jersey victories.