Rhinoceros (abbreviated Rhino) is a commercial 3D computer graphics and computer-aided design (CAD) application software based on NURBS mathematical model, which focuses on producing mathematically precise representation of curves and freeform surfaces in computer graphics (as opposed to polygon mesh-based applications).
Rhino is ideal to use when you are drafting in 2D and creating 3D prototypes from flat stock on the laser cutter. Rhino can also be used to quickly develop parts for 3D printing that will not need complicated revisions. Rhino is exceptionally robust and is ideal for figuring out complicated geometries in three dimensions. It is also simple to create exceptionally clear 2D diagrams from a 3D file. Rhino excels at complex and/or repetitive geometries. Using plug-ins such as Grasshopper, you can develop parametric geometries.
The videos below give a basic introduction to working with Rhino in 2D. Some of the videos use sample files which are in the zip file attached to this post. The two attached PDFs also give a concise and clear explanation of the commands.