Okay, how many pints/litres is it supposed to make?
Do you have a hydrometer?
The method is most likely to be:
Stand can of concentrate in hot water for 10 minutes, to increase its viscosity, then put into a fermenting vessel. Add cooled boiled water to about 2/3 of the total intended volume, allow to cool to room temperature, pitch yeast and fit airlock.
Give it a couple of days until the froth head dies down a bit and then top up to final volume.
Leave it in a warmish place until bubbles stop coming through the airlock.