To ensure a straight cut line, use a square. If the line is not straight, make and cut out a pattern from thin cardboard.
Trace around the pattern to mark the cut line. Mark the cut line with a grease pencil.
Equip the saw with a diamond blade.
Set up the wet saw and fill the water reservoir according to the manufacturer's directions. You can buy or rent a wet saw at most home improvement stores.
Line up the cutting mark with the blade.
Plug the wet saw into the outlet and start it up. Let the saw run until it is at full speed before you start cutting.
Push the tile toward the blade and start cutting. Move the tile slowly so you don't break or damage the tile or the saw.
Check the cut piece to make sure it fits in the area where you need it. If you are confident the tile you cut works, continue to cut all the tiles you need.
If it does not fit, cut the piece again, or choose a new piece and start over.