How does one cut out a retangle or square in a ceramic tile that is 12 inches square - I have four that need to be done on my kitchen backsplash:rolleyes:

You need to use an electric tile saw with a wet blade. You cut from the back so making good measurements is important. The cut on the back will be a plunge cut that's about and inch longer than it needs to be. Since the plunge cut will make a curved slice into the tile the cut will be smaller on the ceramic glazed surface.