in the toolbar category < Tempo> You find the button in the toolbar category < Tempo>
Put down the cursor at the position, at which the Fermata (pause) should be inserted and click on the corresponding button .
Fermatas (Pauses) are symbols. They can be handled like all other Symbols also, edited, moved and deleted.
The length of the Fermata (pause) can be set in the symbol-dialogue (double-click on the inserted sign).