In MPT3 you can find several demonstrations that will help you to get acquainted with the toolbox.
The following demo shows how to construct basic polyhedral set Polyhedron and how to extract some properties of the set.
This demo introduces the concept of a general convex set that is referred to as YSet because it is imported from Yalmip.
The following demo is devoted to a set algebra and highlights some of the new features present in MPT3.
This demo shows how to construct unions of sets and how to access some properties of the union.
Demonstration of set algebra with unions of polyhedra in the same dimension.
The demo shows how to construct Function objects and represent functions defined over polyhedra
and over unions of polyhedra (i.e. to get piecewise functions).
Continue by inspecting Demos on Optimization Interface.