This option is also available under Configuration menu.

The extreme first left box shows options to add new role. Right side box lists all the roles that are added to the system. You can have as much as roles you want to have in your system. A user can be assigned with a role. To add new role, enter the name and click on the 'Save' button. Once clicked, it will be added to the list table (that is visible on the right hand side). Role Name can be edited any time & also can be deleted. 

The default tag in-front of 'Admin' role shows that this is system default entry and it cannot be deleted. Please note that, deleting a role can result in loss of related data.