You should get an account from all three. Once you get the account number, you want to fill them in on your affiliates section. With Google, you earn money if readers who go to your hubs click on your advertising. Don't click on the ads yourself or you will be banned and you won't get your account back. On Amazon and Ebay, you would integrate ad capsules from either into your hubpage. If a reader clicks on one of those and goes into Ebay or Amazon to buy something, you would get a percentage. I suggest you read one of the hubs that talks about this. Just do a search on Adsense, Amazon or Ebay and you can read all about it.