Lay the piece of sod flat on the ground. If it is rolled up, unroll it completely.
Set a two-by-four on the piece of sod to act as a straight edge. Place the wood on the sod in the spot where you want to cut it. If you need to cut the sod in a curved line, use a garden hose as an outline.
Insert the edge of a sharp trowel into the sod, starting at one end of the piece. Lift the trowel and move it slightly over, inserting the trowel into the sod again. Continue lifting the trowel and pushing it down through the sod until you have cut the entire piece.