The Freedraw tool can be used to manually draw lines that can be converted into contours. To enter Freedraw mode select Freedraw Contours from the Insert menu, or select the Freedraw tool from the Drawing Toolbar.
When the Freedraw tool is active, the Freedraw toolwindow will be visible. On this toolwindow you can set the Brush width, delete the last stroke or convert the drawn lines into contours.
To draw straight horizontal or vertical lines you can holding down the shift while drawing.
To erase part of the drawing, you can use the right mouse button as an eraser tool.
When you're satisfied, click on “Convert to contours” to add the contour to the currently displayed glyph (contours cannot be added to composite glyphs). To cancel, just close the Free Draw dialogue with the close button.
The new contour will not be joined to existing contours, even if it was drawn crossing them.