While these models have diminished in mature e-commerce and online advertising markets they are still prevalent in some more nascent industries. China is one example where Affiliate Marketing does not overtly resemble the same model in the West. With many affiliates being paid a flat "Cost Per Day" with some networks offering Cost Per Click or CPM.
Affiliate networks offer you access to multiple (and by multiple, we mean hundreds if not thousands) of individual affiliate programs. They basically work by simplifying the signup process - instead of applying to become an affiliate for a each product you want to promote, you simply apply to join the network and instantly have access to hundreds of different affiliate offers.