Dig out where you want the parking area to be with a shovel, to a depth of 4 inches. Place the dirt in a wheelbarrow as you dig it out for easier removal.
Line the bottom of the excavation with landscaping cloth. Cut the cloth to fit with scissors, and overlap separate pieces by several inches.
Place 2-by-4-inch boards at the margins of the excavation, resting on the 2-inch sides. Nail together the boards with 8d galvanized nails at the corners and cut pieces to size as necessary.
Place 2 inches of medium grade gravel at the bottom of the excavation, and rake it smooth with a heavy rake. You'll need a quarter of a cubic yard of this gravel for each square foot of parking area. Calculate the square footage of the parking area by multiplying the width and length, measured in feet. For example, if the parking area is 12 by 10 feet, the square footage of the area is 120 square feet. You'll need 30 cubic feet of gravel (0.25 times 120).
Fill the excavation the rest of the way with fine gravel and rake smooth. Again, you'll need a quarter of a cubic yard of this gravel for each square foot of parking area.