2 different solutions:

#1: Ad Proxy
They serve ads throughout the web and these websites act as referrals in order to gather statistics about the Ads.

#2: Fake Referrals
The websites use bots in order to fake referrals and appear on analytics tools like Google Analytics or Mixpanel.

Either way, if you want to generate traffic, you'll have to rely on more high-level channels like SEO, PPC or Social.