User roles bundle sets of permissions that apply to what users can do on your board. There are six built-in user roles:
Standard Features. Can access most but not all user features. Cannot change user name or ignore the flood limit, for instance.
Limited Features. Can access some of the user features. Attachments, emails, or instant messages are not allowed.
All Features. Can use all available forum features for users, including changing the user name or ignoring the flood limit. Not recommended.
No Private Messages. Has a limited feature set, and is not allowed to use Private Messages.
No Avatar. Has a limited feature set and is not allowed to use the Avatar feature.
Newly Registered User Features. A role for members of the special newly registered users group; contains NEVER permissions to lock features for new users.
If you want to create a new role, there is nothing from stopping you. ACP > Permissions > Permission roles > User roles. Enter the new role name in the Create role field, then select the role you want to inherit the permissions from in the Use settings from dropdown. Then press Submit. Change the permissions as desired for each tab.
Once a new role is created, you generally want to assign groups or users to the role. Use one of the following paths:
ACP > Users and groups > Users > Manage users
ACP > Users and groups > Groups > Manage groups