What is the process for using a mold to make a concrete patio?
Lay out the perimeter of your patio or walkway with wooden stakes at each corner, with more in between if you've got a large enough area you can't eyeball a straight line.
Remove 1 inch of sod or topsoil, making sure the resulting surface is level.
Mix concrete to the ratio specified on the bag. If you're doing a large area, you may want to do this in batches. The mold should come with instructions about how much concrete it will use for each iteration.
Place the mold in the first location fill each cavity, troweling the top smooth. 
Wait no more than 5 minutes, carefully lift the mold, and place adjacent to the poured concrete for the next "tile."
Continue this process until the patio or walkway area is complete. You may want to rotate the mold each time in order to add variation to your patio.
Brush sand or dry mortar into the joints, and mist with a garden hose.
Cover the concrete for 2-3 days with thick plastic sheeting to keep the surface from drying too quickly and cracking.
Apply a concrete sealer to protect your new patio.


Resources: Lowe's Tutorial, Quikrete Tutorial (PDF)