Saws are cutting tools with teeth or an abrasive edge that work by repeatedly ripping little bits out of a suitable material. They are most commonly used on wood  but special saws and saw blades exist for various materials like metals, stone or glass to name a few.
A disadvantage of saws is that they tend to create a lot of dust and noise...and you sometimes lose a significant amount of material according to the width of the saw blade (the "kerf"). Make sure to cut just outside of your measurements to obtain accurate pieces, not directly on the line!
Many saws have replaceable blades, but even these can be quite costly and may be worth repairing once the time comes. Before sharpening, a blade may have to be set (DE: geschränkt) with a special tool to regain its cutting ability.
"Measure twice, cut once" - before sawing, you'll often profit from making a cut list (Schnittplan) to maximize material utilization. When it gets too complicated for paper and pencil, there are several software options to consider:
- CutList Optimizer (browser based calculator)
- CutList (SketchUp extension]
- MaxCut (more complicated - here's a starter's guide on HolzWerken.net (DE))