I have included 3 images below.

The first one, when it says allosteric effector, that could be the cofactor.  It can attach at a place other than the active site that can allow the active site to work better or just work in general.

The second picture, shows how a cofactor can actually bind to the active site itself. When it is bound to an active site, it allows the substrate to bind (or sometimes just bind better).

A coenzyme works the same way as a cofactor, in fact, a coenzyme is a cofactor, it is just a specific type of cofactor that is organic in nature (as opposed to an inorganic ion for example.

The third picture is just another description taken from the text.