Categories are managed in the "Categories" page of the "Catalog" menu. On the right side This page displays a table with the currently existing categories, with the main information displayed.
Using the icons in the "Displayed" column of the table, you can indicate the ones you want hidden from the customer ( by clicking on the "Yes" icon), thus turning it into a "No".
All the categories are actually sub-categories of the "Home" category.
To edit the "Home" category (or any currently selected category), click on the "Edit" button in the button bar when the table displays the root categories.
To create a new category (or a sub-category of an existing category), click on the "Add New" button from any level of categories.
Make sure to translate each field in every language that your shop supports. In order to do that, click on the little flag language button next to the field, and choose the flag of the language in which you wish to edit the text.