When you create a FIELD, you have several LOCATION options.  5 of those are Tab 1, Tab 2, Tab 3, Tab 4 and Tab 5.   THOSE Location coorospond with Tab 1, Tab 2, Tab 3, Tab 4 and Tab 5 of a specific CATEGORY.. 
 
Each Category has an Item Tabs Options area in which you can set FIVE content tabs (Tab 1, Tab 2, Tab 3, Tab 4 and Tab 5.).     
 
So you can create a Category and it comes default with 1 content tab (Tab 1), however, you can add 4 more ( Tab 2, Tab 3, Tab 4 and Tab 5) that allow you to add an EDITOR to as well as assign multiple custom fields.  
For MORE tabs, there is also the option of creating a Custom Field that is its OWN tab, however, it can't have fields assigned to it as it IS a field....  (there is a TRICK that you can do be creating self placement fields and add those fields to a Custom Field Tab.   
Hope that makes sense now?   Its pretty powerful 
