MDF stands for medium-density fiberboard, which is sold in sheets similar to plywood. It is a low-cost building product that is commonly used to produce furniture, but is used for other purposes, as well. MDF is made from hardwood shavings that are glued together and then heated while being pressed. You can cut MDF with power saws, but the process creates quite a bit of dust, so proper precautions must be taken.
Lay the sheet of MDF on a flat surface and use a tape measure and a pencil to mark where you want to cut it.
Set a saw guide rail on the MDF and move the side edge of the guide until it lines up with the pencil mark. Secure the top and bottom of the guide to the MDF by fastening clamps over the MDF edges. When complete, the guide should be secure and not move.
Put on a dust mask and eye protection, and plug in the cord of a handheld circular saw.
Slide the MDF sheet over the edge of the table until the edge of the saw guide hangs off. If desired, you can also place it between two sawhorses.
Press the trigger on the circular saw and place it at the edge of the MDF, allowing the side of the saw to rest against the saw guide rail. Move the saw forward slowly across the MDF until you cut all the way through the pencil line.
Release the trigger on the saw and allow the blade to stop spinning before setting it down. Unplug the saw and unclamp the saw guide rail from the MDF.
Saw guide rails come in a variety of designs. Refer to the manufacturer's instructions for your specific model.