pinterest

This might be simple, but i just cant figure it out! How are all those pins created in Pinterest? How are all those photos gathered? Who gathers them and who creates them to pins? Can somebody explain me how Pinterest works, who creates the Pins? o_O

Pinterest is great, and so is the private Dropmark service (free, but $48/yr for folders, tags, comments, annotations), but I'd like to create a personal Pinterest on my Mac if possible, in part because I don't like how services like Pinterest track browsing habits via extensions and 'Pin It!'...