Measure where you will cut your pipe. Use a speed square and pencil to mark your cutting line.
Place your pipe into the miter box. Align the pencil mark with the appropriate slot in the miter box.
Insert your saw into the slot of the miter box. Use a saw blade rated for PVC or metal, depending on what you are cutting.
Slide the saw back and forth across the pipe to cut it. Use slow, even strokes to ensure a smooth cut.
File the edge of the pipe to remove rough edges, if necessary. Metal pipe will require filing, while PVC will not.