In order to add a tab click on this button then the add button
Name the title of your tab and the kind of tab it will be.
When you set the page type, you have 3 different options- Content list, Shopify, Spotify
Content list will be the type of tab that you will use in order to house content items.
Within the content list you will need to set the content category. Click on +Add then name the category. Set the tab icon you would like and then click on the cloud in order to save the tab then click the cloud again and
select Save Layout.