Computer Numerical Control, or more commonly called CNC, stands for controlling machine tools per computer. This includes many different tools, like drills, engravers, lasers, lathes, etc. Actually 3D printing is technically CNC too.
To create something using a computer, you will need software to make a drawing. This is mostly done in CAD programs like AutoCAD or Solidworks. Then you will also need software that can translate the design to specific movements, called CAM Software. The output from the CAM software is a G-Code file with machine commands, which can be executed by the softwrae the controls the machine. There are many software alternatives available, but popular ones include Gbrl, LinuxCNC and PyCam.