To sign up for the ClickBank affiliate program you need to use the link below:
https://www.clickbank.com/affiliates/and press Start Here on the main page.
Follow the steps, fill in your personal, billing, and account information
When you fill in your account information, pay attention to the Nickname field. Nickname is actually going to be your ClickBank affiliate ID which you will be using in RSS Ground ClickBank Feeds generator.
When you log in to your ClickBank account, in the Dashboard section you can see your ClickBank Affiliate ID.