To show categories in a Magento store, you ususally need to complete these steps:

1. Create the categories as children of the root category (i.e. not at the same level)
2. Make sure all the categories are active. Inactive ones are shown in gray font. NOTE: If a parent category is inactive it's children won't be shown also.
3. Check that category's property "Use in Navigation" is set to "Yes"
4. Go to System -> Manage Stores, open the "Main Website Store" link and make sure the dropdown for "Root Category *" is set to you root category.
5. Clear the cache and refresh the indexes.

If you want to give a definite admin user to edit categories apply our Magento Edit Lock. In case you want to track all the backend activities of your employees, use our Magento Admin Log extension.