Works best with a Key that has a minimum of: Account, Characters, Progression, Builds.
First you need an API Key
At the top of the page, select Services then My Account
Top right you will see a tab called Applications
Click this and it will take you to your API Key Management page.
Click the Create Key
This opens a new page with options.
Give the Key a Name (optional).
Tick the option boxes you wish the key to give access to.
This web page requires you to have a key that has as a minimum:
Input the API Key you create at the top left of this page.
(I'm sure you can work the rest out your self.)