In the Timeline view, select the cell on which you want to draw.
In the Tools toolbar, select the Pencil tool or press Alt + /.
In the Colour view, click a colour swatch to select a colour.
In the Drawing or Camera view, start drawing.
You can press Shift + Alt as you draw to draw straight lines.
Pencil lines are central vector lines. Sometimes, two pencil lines may look connected because their edges overlap, but if their centerline is not connected, they will be considered an open shape. To make sure the end of your stroke connects to the beginning of your stroke, hold the Alt key when you start or finish drawing a pencil line.