These are default gestures in Pastela.
You can modify shortcuts triggered by gestures using the relative feature.

To learn more on how to edit shortcuts, refer to this page.

Two-finger tap to undo
Three-finger tap to redo
Long tap to activate the eyedropper

Two-finger tap to undo

Tap the canvas with two fingers to quickly undo your latest action.

Three-finger tap to redo

Tap the canvas with three fingers to redo your latest action.
*If there’s nothing to redo, this gesture won’t have any effect.

Long tap to activate the eyedropper

Long tap the canvas to bring up the eyedropper.
The color you select will be added to your palette once you lift your finger.

You can adjust the activation time for the eyedropper in the settings.