They are linked through affiliate links. You go to the websites and sign up to become an affiliate. Lets pretend you want to make links on your website to travelocity flights for airlines….so you go to travelocity.com and look at the bottom of the website. You will see the words “affiliate program” in small letters. Like this: http://i174.photobucket.com/albums/w106/JordanPar23/travelocity.png
Click on that to sign up. Once you sign up, travelocity would give you links for whatever flights you need links for. They may even have links that self update if you want a website that updates itself. So if you want to promote hotels, find a hotel affiliate…check hotel.com…look at the bottom of their page for the words “affiliate” and sign up with them if you want to promote hotels….this is how you do it. Just sign up for affiliates, choose what you want to link to, get the links, and put the links on your site. Then you have to log in to the seperate websites to see how much money you are making. If you sign up for travelocity and hotels.com for example, you will have to sign in to both of them to see how much you have made for each.