A preset is the combination of a blueprint function or variable of an actor with a set value. These can then later be recalled very quickly from the preset panel on the right side
Select the "Preset Setup" tab
Select an actor
Select a blueprint function or variable in the middle pane
Enter in any parameters required for the function/variable.
Press "Execute" to see your changes live in the viewport
"Save as Preset" opens a new window where you can specify a preset name and replace the default image captured from the viewport.
Click Save and your Preset will now appear on the right side preset panel
Presets can be edited, re-arranged & deleted by selecting "Edit/Order Preset" in the Preset panel
Presets can be re-arranged by selecting and dragging them.
Preset names can be changed, update thumbnails, and deleted by selecting edit.