Lay the granite countertop face-down on a large work table. Slip pieces of scrap lumber under the edges of the countertop to raise it up slightly and prevent cutting the table. Clamp the granite and scrap lumber securely to the table. If the countertop extends past the edges of the table, support it with more scrap lumber.
Carefully measure and mark the places to cut the granite to fit the desired project. Clamp a metal straight edge to the granite to act as a guide for the saw.
With the cut complete, unclamp the granite and wipe away any dust or debris from the cutting.