If it were me, I would do the following..
1) QC - pick through them. If you got them for free I would be skeptical about their quality. Remove any rotten or moldy grapes, leaves, or sticks.
2) CRUSH - crush them removing the skins and stems. I would crush the juice into 5 or 6 gallon buckts. Your total yield should be just about 3.5 gallons.
3) TEST - once crushed, I would measure the sugar content (with a hydrometer) and measure the acid.
3) ADJUST - adjust the acid as needed. I tend to NOT adjust sugar.
4) PREPARE - add a dose of Potassium Meta Bisulfite directly to the crushed grapes. A good amount would be 1/4 teaspoon for 3.5 gallons. I would also consider adding a dose of fermax yeast neutriant. You can pick this up on line or at any local beer/winemaking supply shop.
5) COLD SOAK - cover the bucket with plastic and let stand for 24 hours. This is to allow the Potassium meta bisulfite to vent. Place the bucket in a warm area (70 degrees F would be great).
6) RACK - after 24 hours, there should be some sediment at the bottom of the bucket. I would try to syphon the juice into another bucket and disguard the sediment.
7) INNOCULATE - After you rack the juice, you can then add yeast. For good results, you should use a good quality wine yeast. I would recomend Lalvin D-47. Some swear by activating the yeast first, but I never had a problem simply adding the yeast right from the packet. Allow the yeast to simply float on top.
8) COVER - once you add the yeast, cover loosly with a sheet of plastic. At this point, Air is not the enemy.
9) MONITOR - check the wine often. After 2 days, it should be obvious that the wine is fermenting. check the sugar levels using a hydrometer.
10) RACK - when the sugar levels are down to about 1 or 2 percent, transfer the wine into glass jugs and seal with a stopper and fermentation trap. Like before, one goal in this step is to syphon only the liquid wine and not the sediment of dead yeast in the bottom of the bucket.
Let the wine sit for several weeks, until you see the wine clearing with a layer of sediment in the bottom of each jug. Rack the wine again (syphon out of each jug, leaving the sediment behind). After a couple of months, you should have something drinkable.