With the release of the latest version the videos are a bit dated: at this link you will find a short manual that shows how to use the buttons in the new format:
* Write on your Android device as you would on a sheet of paper.
* There are six types of customizable pens with the best digital inking characteristics.
* Insert typed texts, images, geometric shapes in your pages in the most natural way.
* Select and move, zoom, rotate, stretch any object using your fingers.
* Control undo and redo actions with the undo / redo bar.
* Overlay objects and manage their opacity using layers.
* Make the most of an active stylus by configuring erasing methods.
* Work with close writing mode on small screen devices.
* Use gestures to select or delete objects as you type.
* Set the background of any page by importing JPEG, PNG and PDF documents.
* Create new notebooks from the most common document templates.
* Save and load custom sets of paints, pens, typewriters.
* Organize your notes in library folders. Cut, copy and paste notepads and pages.
Supported Android Devices : [4.4–4.4.4] KitKat – [5.0–5.0.2] Lollipop – [6.0 – 6.0.1] Marshmallow – [7.0 – 7.1.1] Nougat – [8.0-8.1] Oreo –  Pie