You can use a mild dish or clothing detergent with a soft scrub brush. Just hang two corners from a tree or house and hose off. There is only one way to fold a sail for storage and that is to flake it accordion style from the foot. Then roll the sail so it will fit in the bag. Make sure the sail is totally dry before flaking and bagging.
It is also a BIG help if you list the boat and location with your avitar. A dingy sailor often rolls sails, while that is not practical for larger boats. But we can't tell what you have, which puts us at a disadvantage.
I always rolled my sails when I owned a Tuna 20 and bagged them after every sail. I flake
the sails of my 24 now for storage only because the bags are smaller. Longer bags are on my to do list this summer albeit near the bottom of the list. Rolling the main may be a moot point because it's flaked on the boom during the season.
Whatever you do with them, don't leave them in your garage where mice and squirrels can get to them. Under your bed in a platic tote with a couple of sticks of cedar, like Grammy used to do with wool sweaters. They're worth hundreds or thousands of dollars.