A machine tool in PowerMill is a mathematically modelled representation of an actual machine tool with physical axial limits and axial relationships. Each axis of a machine tool is modelled with associated surfaces. They are used for collision checking during simulation and provide a visual aid of how a part is going to be machined. This helps you to create safe toolpaths.
You can access many of the functions you need to work with machine tools from the Machine Tool tab on the ribbon.