A doodle element is a user-made piece of art (in the optimal case...) or a quick sketch.
Consider putting a Shape Element behind a doodle to act as a background.
Any doodles created are stored as bitmaps in
/sdcard/Zoom/doodles/ in case you wish
to use them outside Zoom.
The second row is the palette. The leftmost (black) palette colour selects erase mode, the others just change the drawing colour.
To change a palette colour, just long-click on it. You can't change the erase colour.