Look for the settings page in the menu ☰. This page has a Roles tab where you can add new or edit existing roles.
Authorized users can easily define many different roles, each with it's own set of rules. To create a new role select the + button on the right-hand side which will open a dialog. In this dialog you have to define a name for the new role and select rules. The rules are divided among several tabs for an easier overview. Select per tab which rules apply to the new role you're creating and click save. Now this role will be available when adding a new, or editing an existing user.