The Green Plus and Red Minus icons in the sidebar are used to:
Green Plus: This will add new items in the side bar when selected. Example: In the Patient tab, the Green Plus makes it possible to add a New Account or a New Patient.
Red Minus: This will remove existing items from the side bar. Example: In the Schedule Ability, the Red Minus makes it possible to permanently delete appointments.
If one or both of these icons are greyed out, then it is not possible to add or remove specific items.