How do I change the weight / thickness of handwriting, highlights, and shapes?
You can select a weight / thickness for handwriting, highlights, and shapes in the tool picker before drawing / writing.
To change the weight / thickness of handwriting, highlights, and shapes that are already on the page, you must first select the object(s). Then tap the weight / thickness icon () at the top of the screen, and select a new weight / thickness for the object(s) you selected.
For a video tutorial about changing line weights, see Squid - Tools Overview.