Step 1 - First you need an account for the Google Affiliate Network so visit this site and click on the Sign up as a publisher button.
Step 2 - If you already have an AdSense account select that radio button and sign in with your AdSense login details. If you don't have an AdSense account you will need to follow the online procedure to apply for one. The reason for this is that the affiliate payments all go through AdSense.
Step 3 (once you have an AdSense account) - You will need to complete the details of your primary website and the methods you use for promoting your site such as email marketing or search engine marketing. After all, if you don't promote your site, there's no point in advertisers placing their ads there. You can also list any additional websites you may want to publish adverts on. You will also need to agree to the program policies and terms and conditions.
Step 4 - You'll receive an initial email confirming receipt of your application and within a day or so you should receive a second email telling you whether your application has been approved. If it hasn't you can try to find out why but you could run into difficulties. If you are approved, proceed to Step 5.
Step 5 - Log on to the Google Affiliate Network and search for advertisers who are a match to your website. You can use the Payout Rank filter to find the best paying programs if you want to. When you have applied to the programs that interest you, you will have to wait for approval from most of them (some grant immediate approval). This can be a very slow process - as I write I have been waiting for three weeks for a response from two advertisers while two others to which I applied on the same day responded within 48 hours.
Step 6 - Check out the available links from your approved advertiser programs. Some advertisers allow you to link to specific pages or products but the method is quite well hidden - see Step 7.
Step 7 - Linking to specific pages or products. Click the Advertisers tab and choose browse existing. Click on the advertiser name to reach their profile page. If they allow you to create your own links there will be a Create Links button next to the View All Links button at the top of the page. From there it's quite simple to use; just enter the page you want to link to and a few other details and click Save.
Step 8 - Insert the code for your chosen links on your website and promote it any way you know how. A good, free way is to review the product you've chosen in an article directory and link it to a page on your site with a further article about the product which contains your affiliate link.