Drawer glides are those metal units on the sides of drawers that allow them to move smoothly in and out their cabinets. Sometimes, they need to be added or replaced. Older furniture is often harder to open and close because they don't have glides attached. Sometimes the drawer glides don't last nearly as long as the drawers themselves because it's easy to bend the supports down with an open drawer.
Slide the drawer into its cabinet to see how it fits. Remove the drawer.
Measure from the top of the drawer, on the right side, to one-fourth of the way down from the top, and mark a line with the pencil. Repeat this action, going from the bottom of the drawer to one-quarter up. Repeat for the left side. Apply the level on both lines, in the front and in the back, and top and bottom, to be sure that everything is square.
Place a drawer-side slide on one of the lines and check it with the level. Screw the drawer-side slides on the drawer, inserting the screws through the holes in the slides. Repeat this procedure for all of the slides. Wait to tighten everything until you check it all with the level again.
Slide the cabinet-sides of the slides onto those installed on the drawer.
Turn the cabinet on its back and slide in the drawer so that it meets the back of the cabinet and sits there.
Mark the bottom lines of all of the slide pieces on both sides of cabinet's interior--everything should be touching now--using the carpenter's square. Remove the drawer, and double-check that your lines are straight.
Remove the cabinet-side pieces from the slide mechanisms, and screw them onto the lines inside the cabinet, using the holes in the mechanism. Again, don't connect it tightly until after you have made final adjustments.
Reinsert the drawer and check its fit, after which you can screw everything together tightly.