Assistance refers to the description of an object's inlets and outlets. When Assistance is checked in the Options menu, descriptive captions appear near an inlet or outlet as you mouse over it.
As you move the mouse over an object's inlets you'll notice that some are blue and some are red. Blue inlets are known as "cold" inlets. They do not produce any output (out the object's outlets) directly. Red inlets are "hot" inlets and can produce output when you send a message into them.
If you make a subpatcher or abstraction, you can add your own assistance messages to describe the patcher's inlets and outlets.