The Minimap Object allows you to create RTS-like minimaps with ease. It allows you to chose from lots of different properties such as different types and shapes.
The map is the commonly used minimap that displays a miniature of the entire map while the radar displays a smaller area around a certain point.
One of the main differences is that you no longer have to plot your enemies (or whatever) every frame. Now you simply add them to the extension with a set of properties and the extension will handle all drawing for you. This method results in less CPU usage as less data has to be sent from MMF to the extension every frame loop.