Where is the belt tensioner located?

The single belt loops around all the different pulleys on your engine, but one pulley has a tensioner arm, which will be the only pulley the has a square, 3/8-inch hole in the center. That hole is for a 3/8-inch ratchet nub, the part that holds the socket. Place the nub of the ratchet wrench into the square hole of the tensioner pulley and rotate the wrench. Try both directions, which will require you to flip the selector on the wrench to the opposite direction (so you can loosen or tighten). The tensioner will move only in one direction, and when moved will release its grip on the belt. Make sure you study how the original belt wraps around the various pulleys.