Lay the drawer on its side. The slide needs to be flush against the drawer’s bottom edge. The slide’s thicker, squared end should be flush with the drawer’s front edge.  Undermount slides attach to the bottom of the drawer, one each on the left and right edges. For center mount slides, use 1 per drawer. The slide attaches to the bottom of the drawer, running from front to back along the center. Draw directly on the drawer. Create a thick, dark line right above both ends of the slide. Also mark the spots where the slide will be screwed to the drawer. The slide will have a screw hole at both ends. Get an electric drill with a drill bit  approximately 2⁄3 in (1.7 cm) wide. Drill about 1⁄2 in (1.3 cm) into the screw spots you marked earlier. Drilling the holes in advance prevents damage to the cabinet when you add the screws later. Set the slide back on the drawer. Align its top edge with the mark you made earlier, adjusting the slide so the holes are over the spots you drilled. Place a 1⁄2 in (1.3 cm) screw in each hole. Fasten the slide in place with an electric screwdriver. To avoid damaging the wood, tighten the screws gradually. Stop when the slide feels firmly in place and doesn’t wobble. Find the other small slide piece. Flip the drawer over so the other side is facing up. Then, line up and attach the other slide the same way you did with the first one.
Align the smaller slide against the bottom of the drawer. Mark the slide placement in pencil. Predrill holes into the drawer. Screw the slide to the drawer. Attach the slide on the other side of the drawer.