How do I use a lensatic compass?

I recently got a satellite finding kit to help me put up a dish, one part of the kit is a compass with some parts that I do not know how to use (in the end I just pointed the dish in the same direction as the neighbours and fine tuned it with the meter).

On Googling it is apparently a lensatic compass and it looks like like this:

It has a fold-out wire, another fold-out lens and a movable face with lines painted on it.

The Wikipedia page mentions taking angles from a map but it isn’t very detailed, obviously the needle points to magnetic north but I am interested in the other parts, can anyone tell me how to use them please?

Thanks in advance to anyone who replies.

Does this help?