A leveling screw is a very useful piece of hardware that comes with many of the modern appliances and furniture pieces.
What it is
Generally, an appliance or piece of furniture will have at least one leveling screw and it is usually located in the front. These screws which are really an extendable piece of the leg, typically have a plastic or Teflon ring around them and act as a foot. There are 2 basic types of leveling screws. One style is just a simple screw that requires a screwdrivers. The other style has a nut that when tightened by a wrench raises or lowers the leveling screw.
How to Use it
Leveling screws adjust up and down to keep an item from rocking back in forth. Use small adjustments with a wrench or pair of pliers until the piece is level. When there is more then 1 screw adjusting the piece becomes a little more involved, but it is easier to keep level.