They are usually found in one of three stages: green, yellow, or black.
Deep fry these and make chips. Drain oil and season with salt as soon as they come out of the oil. You can also use season salt, freshly grated garlic in a little olive oil, or your favorite seasoning.
Next is the ripe, soft plantains. These are yellow with black spots or all the way black with barely any yellow. Just cut on the bias about 1/2 inch thick. Fry on medium high heat about 325 if you have a fancy fryer. Then drain on paper towels or brown paper bags.
These are made in several cultures and liked by many. Give it a try!