Using SlidePilot's drawing tools, you can draw on the current slide. To display the drawing tools, press the D key or select Moderator → Draw.
You can then choose any of the predefined color and draw on the current slide. If you want to draw on a white canvas, press ctrl + K or go to Moderator → Canvas Mode. To clear the drawings on the canvas, press ctrl + C go to Moderator → Clear Drawings.
Note: When you're in drawing mode, you cannot switch slides or change the layout. To continue your presentation you have to exit the drawing mode. Once you exit the drawing mode, the drawings will be gone.