Go to your "Categories" area of your E-commerce module, and click add.
The path looks like this: YourDomain.
CategoriesSee screenshot:
The area looks like this:
Click on "Add Category" to create a new category.
Once you have 1 Category created you can "export to CSV" and create your Categories in a CSV file, then import them. This is recommended if you have a large number of Categories. Also you can Backup your Categories by exporting to CSV and saving the file on your Computer.
When you are on the add category screen you will be able to set the category name, whether its active, make a description for the category, add a picture that represents the category, Select where in the tree structure it appears and set any shipping restrictions. You can also add products that will be included in this category.
See screenshot: