That's a huge subject, actually -- long and short, you do have to sign up for affiliate accounts through Adsense, Amazon, eBay, and/or Kontera (pick and choose which ones will work best for you) and those are how you earn. Eventually the Hubpages ad program is also supposed to be opening up to more and more people, so that may be an option in the future as well. That said, selecting lucrative subjects, marketing your hubs, building successful hubs, etc. is all part of how you make money on hubpages as well. I'm in the process of creating a series of hubs on this subject, and I suspect that about 20 should allow me to adequately cover the basics.