The most common tile cutter looks like a pencil and has a tungsten carbide tip to score the tile. To snap cleanly, place a matchstick under the scored line and press down evenly on both sides of the tile. A neat break should result.
The tile cutter scores with a cutting wheel. Place the tile in the jaws of the tool and gently squeeze the handles, pincer-fashion, to make a clean break. To mark an end tile for cutting to size, place it in position (front surface against wall) making sure one edge of the tile butts into the wall. Measure the distance from the end of the wall to the preceding tile in the row. Mark the width required in pencil, first on the reverse, continuing round the edges to the front face when you have turned the tile round. To join up these lines correctly place the tile face up on a firm, flat surface and using a metal straightedge (your try square is ideal) align the two pencil marks and score through the glaze with your cutter. Use one of the two cutting methods described. If really thin sections, less than 10mm thick, have to be cut, score deeply along the marked line and with pincers nibble away gradually at the waste portion. Never be tempted to take off a huge chunk in this way as the tile will break. Use this method, too, when cutting out L-shaped or curved sections. Make a card template (pattern) of the shape required and transfer it onto the tile. Projecting pipes are tricky to tile around so use a template again. The safest way to tackle the job is to cut the tile in two, removing from each portion an arc to suit the shape of the pipe. When the two portions are positioned together round the pipe, the joint will not be obvious.