The Role field is a dropdown next to the person's name in the task list.
Once roles are set, you can use filters to view items that include tasks with a specific role.
To enable roles, follow the steps which are detailed here.
- Make sure that the "roles" feature is enabled
- Go to the Initiative Settings page
- Select the 'Members' section from the left menu
- Click "Edit" located next to a member's name to choose/add roles.