The first thing you need is to install the extension. Go to the chrome web store and click on the "ADD TO CHROME" button.
When the extension is installed, a helpful thing is to pin it to the extensions bar. Click on Extensions button in chrome, find Affiliate tools extension and pin it
Now you need to configure affiliate ID for stores. Go to extension options, select platforms, find the store you want to use, and fill your affiliate ID (link key, referral id, etc, depending on the store).
You can click on the question mark next to the store name, to read how to get an affiliate id for that store. If you have a bit.ly account and want to use it to shorten links, you will need to configure a generic access token.
Go to Profile Settings / Generic access token. Enter your password and click "GENERATE". Copy the token you received and paste it in options. Your extension is now ready to use. When you find interesting product you would like to generate affiliate link for, just click on extension icon