It depends on what types of grains are in the bag. Does it list the grains at all? I would guess if it's an extract kit then those are steeping grains, but that's just a guess.
If they are steeping grains then you bring a gallon of water to about 160F, turn off the heat, put the grain inside a steeping bag and put them in the hot water for about 30 minutes with the lid on the pot. Pick the grain bag up after 30 minutes and let it drain over the pot (don't squeeze the bag) until it starts to drip once every couple of seconds and then discard the drain. Add more water to get to your boiling volume and brew away.