To install side drawer slides, you must determine the proper mounting locations for both the drawer and cabinet sides of the slide assembly, and then secure them into place. This requires careful measurement of both the drawer and cabinet to ensure they line up correctly.
First, line up the left slide assembly to its proper position against the drawer. Make sure the back of the drawer slide is facing the drawer. Measure the drawer and center the slide, marking with a pencil all four corners where the slide will be installed. Do the same with the right slide assembly on the opposite side of the drawer.
Disassemble the left slide assembly to separate the drawer and cabinet sections. Line up the drawer section against the markings made earlier and mount it into place with the included screws. Install the right slide assembly to its proper location on the opposite side.
Reassemble each side of the slide assembly to its appropriate cabinet slide and line the drawer up inside the cabinet. Make sure it's positioned exactly the way you would like the drawer to sit when it's installed, taking into account any necessary clearances to accommodate the drawer front. Mark off the area on each side of the cabinet where each cabinet slide is sitting, both front and back.
Remove the drawer and once more disassemble each side of the slide assembly. Line up the left cabinet slide to the markings, and install it with the included screws. Repeat these steps to install the right cabinet slide. Then slide the drawer into place and ensure that it's properly positioned.