Adding your first addon

Click on the gray + icon 

The Addon Library Catalog will open up where you can navigate between categories on the left side and choose from any of the free addon on the left. 

When you hover over an addon you will see an install button which you can click to install and click again on the addon to place it in the page. 

Once you click on the addon you will see a configuration popup which you can fill in with the details of your addon.
In some cases you will also have an ITEMS tab so be aware of it and fill it in accordingly.