Lay the 1-by-4-by-36-inch boards out on a work surface. These are the gate pickets. Orient the gate boards vertically and parallel to each other. Space them evenly across a 35-inch-wide span. Use a tape measure to ensure that they are evenly spaced.
Lay one 1-by-4-by-35-inch cedar board across the top and bottom ends of the gate pickets so that they are in 6 inches from each end. These boards are perpendicular to the gate pickets.
Hammer two evenly spaced finish nails through the two 1-by-4-by-35-inch boards at each gate picket joint to secure the gate pickets to the boards.
Position the 1-by-4-by-96-inch board diagonally from the bottom right corner edge of the top 1-by-4-by-35-inch board to the top left corner of the bottom 1-by-4-by-35-inch board. Mark the edges of the 1-by-4-by-35-inch boards onto the 1-by-4-by-96-inch board where they intersect with the 1-by-4-by-96-inch board using a pencil.
Adjust the miter saw to cut along each pencil line on the 1-by-4-by-96-inch board. Cut the board at each pencil line with the miter saw. This is the diagonal board.
Fit the diagonal board between the two 1-by-4-by-35-inch boards to form the "z" support structure for the gate. Hammer two evenly spaced finish nails through the diagonal board into the gate pickets at each gate picket joint along the length of the diagonal board.
Align one hinge on the left side of the gate assembly. Position the top hinge 6 inches down from the top edge. Position the bottom hinge 9 inches up from the bottom edge. Drive the screws included with the hinges through the mounting holes into the gate assembly with a screw gun.
Hold the gate in place between the fence posts in the opening. Drive the screws included with the hinges through the mounting screws into the fence post to fasten the gate to the fence post.
Close the gate. Align both halves of the gate latch on the side of the gate that opposes the hinges. Drive the screws included with the latch through the mounting holes into the gate assembly and fence post respectively to secure the latch to the gate and fence post.