Mix the concrete according to manufacturer's instructions. Pour the concrete into the concrete form, and trowel the concrete with the concrete float so the surface is smooth. The surface of the concrete will appear slightly wet when the concrete is properly finished.
Cut a piece of the 1/2 inch plywood approximately twice the size of the word or letters that will be stamped into the concrete's surface. Judge the size of the plywood based on the size of the 3-D letters used to make the template.
Attach a piece of the 2 by 4 to the backside of the plywood using the all-purpose screws. Screw the narrow edge of the 2 by 4 directly to the plywood. The 2 by 4 will serve as a handle for the plywood template.
Draw a line along the front side of the plywood template, and arrange the 3-D numbers and letters on the line to form the desired word. Arrange the letters to spell the word in reverse, with each letter and number also reversed. When the template is held up to a mirror, the letters should appear in the correct order.
Using the drill, screw the letters and numbers to the plywood template using the 1-1/4 inch all-purpose screws, so that they spell out the desired word. Before stamping the letters permanently into the concrete, hold up the template to a mirror and look at the letters. In the mirror, the word should appear properly aligned, with all the letters facing the right direction, rather than in the reversed position.
Spray the surface of the letters with a heavy coating of silicone spray. This will help prevent the concrete from sticking to the template when it is removed.
Press the plywood template into the wet concrete until the plywood surface comes in contact with the surface of the concrete. You will have to wiggle the template back and forth to get it to set down into the concrete.
Keep the template in place for a short amount of time. After five or six minutes, carefully remove the template by lifting the plywood directly upward. The template may need to be wiggled a bit to free it from the concrete. Do not move the template so much as to distort the letters, which will remain imprinted in the concrete as it drys.
Allow the concrete to dry without being disturbed. The letters stamped into the concrete surface will remain as the concrete hardens.