Stake out the area where the patio is going to be. Run twine to the stakes to create an outline.
Dig out the space inside the twine. Dig down 6 inches and remove the dirt for use elsewhere. Try to make the hole somewhat smooth.
Pour gravel into the space to a depth of 2 inches, maintaining the slope of the ground. Tamp down the gravel.
Cut 2-by-4-inch boards to fit the dimensions of the area that was dug out. Have the front and back boards several inches longer so that the side boards can attach to them.
Place the boards around the hole and screw them together with 3-inch screws.
Tap stakes into the ground on the outside edge of the frame every 2 feet. Drill screws through the stakes and into the frame with 2-inch screws
Check the the frame to ensure it is level. Place a board across the frame and put a level on it. Tap the attached stakes in or pull them slightly out of the ground to adjust the frame until it is level.
Mix cement mix in a wheelbarrow to pour into the hole. There are several types of mix that you can use from basic to crack-resistant. Follow the directions on the package.
Pour the concrete into the hole and smooth it flat by running a board across the edges of the frame and dragging it. Let it sit for awhile and then smooth over with a trowel for a slicker surface. Let the concrete dry for a day. Keep damp by watering it once a day for three days. This will cause a slow cure that will create a stronger concrete surface.