Screen hotspots are rectangular areas added to Overflow screens that indicate an interaction to go to another screen (on click). Those areas become interactive in the Overflow presentation, as long as a connector is attached to them.
You can add hotspots from the Insert menu, or by using the 'H' keyboard shortcut.
In the Editor hotspots are resizable: handles appear when selected. Magnets appear on hover, as with other elements. You can cut, copy, paste, duplicate hotspots. You can also multi-select and align, arrange. Hotspots are bound within the screen limits.
In the presentation, they behave just like any other interactive screen layer (as long as they have a connector attached). They appear by holding SHIFT or by clicking on empty space on a screen.