Almost every tiling job requires that you cut at least a few tiles. There are several ways to do this.
For small tiles, a handheld scoring cutter is a good choice. Place the cutting wheel on the edge of the tile where you want to start the cut, push down with your opposite hand and move it across the tile.
Grip the tile with the cutter. The two "ears" apply pressure on either side of the cut when you squeeze the handle, breaking the tile along the score line.
For larger ceramic tile, a bench top scoring cutter is a good choice. The principle is the same.
A tile saw is a circular saw with a sliding platform and a pump that circulates water over the wheel keeping it cool as it cuts. It is the only effective way of cutting large or thick tiles, or tiles made of porcelain. A tile saw is also the best choice if you have a lot of tile to cut. You can rent a tile saw for $30 to $45 a day.