This video explains how to cook a Spanish tortilla. Peel the potatoes and cut into thin round slices. Slice peppers, onion and parsley. Heat frying pan under High-Medium and fry potatoes. Do not allow potatoes to become crisp. Mix eggs in bowl, add cooked potatoes, onions, peppers, parsley, black pepper and salt.
Warm stove to Medium. Pour enough oil to cover the bottom of the frying pan entirely. When oil begins to spit, pour in tortilla mixture. Allow the top of the tortilla to become firm before attempting to flip over.
To flip over, find a large plate and cover pan. Hold pan with one hand and the plate pressed against it with the other. Then, flip the tortilla onto the plate.
Put pan back on stove and put fire on Low. Slide tortilla (now with the other side facing down) into the pan. Allow 5 minutes for the bottom to get firm. Taste an edge to make sure tortilla is cooked all the way through.