Determine the size of the gate by measuring the opening in the fence. The gate should be about 4 inches smaller so it swings freely.
Make a frame of 1x4-inch lumber that is 4 inches smaller than the gate opening and the same height as the fence. Attach the corners with galvanized L-shaped corner brackets and galvanized wood screws.
Cut the cross members one inch shorter than the width of the gate.
Use a reciprocating saw to cut holes in each upright board of the gate in which to lay the horizontal cross members. The holes should be large enough to hold the 1x4-inch cross members and should go all the way through the uprights. Position the holes so the cross members are the same height as the cross members in the fence.
Slip the cross members into the holes in the gate's uprights. Secure with galvanized wood screws.
Attach hinges to one of the gate's uprights. Position one about 3 inches from the top and the other about 3 inches from the bottom. Use galvanized wood screws to attach the hinges.
Have a helper hold the gate in position. Attach the top hinge with one screw, then attach the bottom hinge with one screw. Insert the remaining screws into both hinges.
Mark the position of the latch on the gatepost and attach that side of the latch first. Then mark its corresponding position on the gate and attach that part.