Though not the ideal tool to use, a miter saw can be used to cut tile if a diamond blade can be installed. However, make sure that the blade is installed so it spins in the correct direction. If it spins backwards, the blade will wear out prematurely. The job will create a lot of dust, but connecting a household vacuum or a wet/dry vac to the miter saw's vacuum port will eliminate that problem.
Mark the tile where the cut needs to be made. The mark can be made with a pencil or a permanent marker.
Hook a household vacuum or a wet/dry vac up to the miter saw's vacuum port.
Place the tile down flat on the cutting surface and line the mark up with the blade. Make sure the tile is snug against the fence of the miter saw.
Power up the saw and allow the diamond blade reach full speed. Cut through the tile slowly. If the tile is too large to cut through in one pass, turn it around and finish the cut.