Select Fermata (also known as a General Pause or just a rest) and tap the note or rest on which you wish to place the fermata.
If there are other notes or rests on the same beat in other staves, StaffPad will place a fermata on those staves as well.
You can move fermatas on other staves freely by dragging the fermata with your pencil and individually delete each of these fermatas should you choose to do so. Once a fermata on a different staff from the originally placed fermata is moved from the same beat the original fermata was placed, it can be deleted without deleting the original fermata that was placed.