Set the piece of wood you will be cutting into blocks onto a sawhorse. If you want the blocks a certain length, measure this length onto the piece of wood and mark it with a pencil.
Hold the saw on the first pencil mark. Place your thumb against the side of the blade to help stabilize the saw for you first cut.
Pull the saw blade backward to start making the first cut. Move your thumb and push the saw forward to continue the cut.
Saw gently back and forth until you are all the way through the board. Use the entire length of the saw to minimize the work required from you. Once the block is cut off, slide the board down the sawhorse and begin cutting the next block.