Designing parts, assemblies and drawings before making them.
A starting point
CAD means computer-aided design. It turns an idea into a drawing or a three-dimensional model with defined dimensions. You can examine how parts fit together, change a measurement and work out clearances before cutting material.
A typical starting point is a dimensioned sketch. From it, you build a solid, add holes and other features, and bring parts together as an assembly. The result can become a workshop drawing or provide geometry for CNC machining, 3D printing or laser cutting. Material, tolerances and the manufacturing process still shape the final design.