The selected unit may be commanded from the toolbar or by  clicking on the map directly. On the toolbar  four buttons under the name of the selected unit allow you to:

Disband a civilian unit (unit icon with arrow pointing down)
Since this decision is final you will be asked to confirm it.

Cycle to the next unit (unit icon with arrow pointing to the right)
Use this command if you want to give the unit an order later in the turn.

End the turn of the selected unit (unit icon with exclamation point)
The unit will be available next turn.

Put the selected unit to sleep (unit icon with letter z)
The unit will be removed from the unit cycle until you select it manually on the map.