The screws are for adjusting the height of the rollers on a sliding door and to ensure movement of the door. Typically found on the edges (bottom) of the door, these adjustment screws allow you to move the rollers up or down as needed. To make adjustments, you can use a screwdriver turning it counterclockwise to raise the rollers and clockwise to lower them. It’s important to locate and access these adjustment screws, for maintenance and adjustment of your sliding glass door. If you can’t see them away they might be concealed by plugs that can be removed for access. In some situations, you may need to remove the entire door itself to reach and adjust the rollers.