When working with concrete be sure to keep skin covered by wearing gloves and long sleeves. If concrete gets on your skin it can burn it within minutes. Making a thick slab of concrete will require you to keep your skin covered, but process is quick and shouldn't take very long. During a hot and sunny day the slab of concrete will need to be periodically moistened for best results.
Make framework. Purchase lumber in order to make a square around the area where you want the slab. Buy 4 planks about 6-foot long and at least 8-inches thick depending on the thickness wanted for the slab. Nail the four pieces of wood together to make a perfect square.
Measure corner to corner of the framework. This will make sure that it is perfectly even.
Decide how thick you want the slab. The thicker the slab the sturdier it will be. Most concrete slabs are at least 3-inches thick. In order to have a 6-inch thick slab for instance, you will need to make sure that the area the slab will go in will be at least 6-inches deep. Dig the dirt out and then make sure the ground is level.
Set framework in place. Hammer each corner into the ground and put braces in the front and back of each side to help brace the framework.
Water dirt before pouring concrete. This will help keep moisture in the concrete and help prevent it from cracking as it dries. Pour the concrete into the framework area. Tap with the hammer on framework as the concrete settles in order to vibrate it and elliminate air pockets that would cause cracks.
Use straight piece of wood or a level to level off the concrete. Smooth out the concrete with a trowel and as it hardens be sure to continue to re-trowel the concrete for the smoothest appearance.