Categories can be restricted to be accessible from certain customer groups only, categories can be password protected to allow only users with the a specific password to access them.
The category access settings section:

At the category access settings section you can set and edit all the properties of the category regarding the access of the category by customers.
The following fields are available:
| Field | Description |
|---|---|
| User Group for Product/Category | Specify whether this category is for special user groups only Please note: You need to setup customer user groups for this function, otherwise only the default “Free” group will be available. |
| Password Protected | Specify a password for this category. If specified, this category can only be accessed when a password is entered at the storefront. |
| Access Password | The access password, for a password protected category. The password protected setting needs to be enabled, for the access password to be used at the storefront |