Cutting floor and wall tile with a tile cutter should not be a difficult job.
First, pull the handle all the way back. Place the tile into the tile cutter squarely against the tilestop. Bring the wheel up to the tile at the mark where you need to cut. Hold the tile as you push the handle forward with medium pressure. Score only once. Use only medium pressure pushing down on the handle while scoring. The wheel will drop off the front of the tile into the docking area. Push down on the handle until the tile snaps.
For a complete video walkthrough of the above steps, watch this tile cutting tutorial.