The advertisers and publishers are doing same stuff which is business and you need to be that perfect and smart.
Below are some full difference between advertiser and publisher just read carefully.
An advertiser, also known as a merchant or retailer, is a Web site or company that sells a product or service online, accepts payments and fulfills orders. Advertisers work with publishers to promote products and services in exchange for a commission on leads or sales through a variety of methods.
They go to AdWords and start a campaign to promote/advertise some product! They win when they sell their product (or affiliate product)
A publisher, also known as an affiliate or reseller is an independent party that promotes products and services of an advertiser in exchange for a commission on leads or sales. A publisher displays ads, text links, or product links on its Web site, in e-mail campaigns, or in search listings and is paid a commission by the respective advertiser when a visitor takes a specific action such as filling out a form, making a purchase or subscribing to a service.
they go to AdSense, get some ads (java code in this case) and put it on their site. They win when someone click on their ads (or impressions etc.)
You join both of them and you will know it very soon…you can make money from both.