The roles for a given community are defined by the template that was used to setup the community originally and reflect normal kinds of roles and names used within that kind of community.
Roles can be added for a member by navigating to the particular member view in the web interface or on the mobile.
Click or tap on the configure icon and then click on ‘Add role’ in the permissions tab to add a new role. In the web interface select the role you wish to add; in the app, swipe the role to the right.
Existing roles can be removed by clicking the delete icon or swiping to the left.