The Change Arrow tool lets you change the endpoints of an existing Arrow. It can only be applied to Arrows. Select the tool on the Lines tool tab. The Arrow Settings will then be visible at the bottom of the tab.
Modify the settings, return to the canvas, and then simply tap an existing Arrow to apply the new settings. Here’s an example:
The Null tool does nothing. This may not sound very useful, but it is if you just want to point out features of the canvas to someone without changing it. A small transparent circle is displayed at the point you’re touching. This might be useful if you’re displaying the device screen on a separate screen. Think of it like a laser pointer for presentation.