Astrophotography question? OAGs?

How do off axis guiders work? I know they have a CCD that captures light from the guide stars which they use to guide. But do they have to be connected to another telescope and so on. Im doing a project on glinting satellites ranging between magnitudes -6 and 12 and I feel an OAG would be easiest, but I am not sure of the dynamics that would make my life easier. Any help is appreciated. Thanks!!!