Draw tool

Choose the Draw Tool in the Toolbar (A/X button) and select one of the available brushes in the opened menu. You can set color and material for it and adjust the brush size pulling the stick on your dominant hand to the right or left.

To use the Draw Tool press the trigger button, draw something, and release the button.

Select the stroke with the Select Tool and trigger button to open the Object Inspector and change this stroke's properties such as opacity, size and position, color, and material.

The Object Inspector for the stroke in the Web editor. It looks the same in the Shapes app.