We have so many Mandarins from the little tree in our backyard that we really couldn't just eat them all. We gave some away and then decided to make some Mandarin Marmalade.
Here are the photos of what we did:
First, get about 2kg of Mandarins.

Next, peel them all, and get all the parts sorted and prepared (don't discard the pith, seeds, and peel as they are important for texture and taste):