The first joint fledgling cabinetmakers usually learn is the rebate joint. This simple joint is an L-shaped groove used to make boxes and cases. The groove cut in one board is usually the same depth as the thickness of the board to which the grooved board will be joined. Rebates are also used to hold the glass in mirror frames. Traditionally the joint was cut by hand with a specialised tool called a rebating plane. It can also be cut on a table saw using an adjustable, multiple piece "dado blade" but now most woodworkers cut rebates with a router.
Unplug your router. Loosen the router collet nut with the collet wrench that came with your tool. Insert a router rebating bit into the collet that is the same size as the rebate you intend to cut.
Tighten the collet nut with the collet wrench. Turn the router upside down. Fully extend the router plunge mechanism
Adjust the cutting depth of the rebating bit by holding a router depth gauge over the bit and turning the depth of cut adjustment on your router until the bit just touches the bottom of the gauge. Lock the depth of cut adjustment according to the instructions that came with your router.
Clamp the board you intend to rebate to the edge of a flat work surface, using two C clamps. The board should overhang the edge of the work surface. Position the clamps so they will not impede the movement of the router.
Plug in and position the router so you will begin cutting in the middle of the joint and not at the end of the board. Stand at a right angle to the board you intend to cut.
Start the router, wait a few seconds for the bit to reach full speed and slowly plunge the bit into the wood using the router plunge mechanism. The slower you force a router bit to cut, the smoother the cut will be.
Slide the plunged router slowly to the right, until you cut the rebate joint all the way through the right end of the board. Turn off the router.
Reposition the router over the existing portion of the rebate joint. Turn the router back on, plunge the bit using the plunge mechanism and complete cutting the joint by slowly sliding the router all the way through the left end of the board. Turn off and unplug the router.
Check the fit of the two boards you intend to join. Adjust the router and make additional cuts as needed.
Apply wood glue to both sides of the rebate joint and secure the joint with pegs, biscuits, screws, nails and/or frame brackets depending on what you are building.
Router bits are sharp and spin at up to 30,000 revolutions per minute.