To draw in a glyph use a pen like object
To add or insert points use appendSegment or insertSegment

glyph = CurrentGlyph()
glyph.clear()
## grab the pen of that glyph
pen = glyph.getPen()
## draw with the pen
## this draws a rect
pen.moveTo((100, 100))
pen.lineTo((100, 200))
pen.lineTo((200, 200))
pen.lineTo((200, 100))
pen.closePath()

## grab the first contour
contour = glyph[0]
## append a segment
contour.appendSegment("line", [(150, 50)])
## insert a segment
contour.insertSegment(2, "line", [(50, 200)])
contour.insertSegment(3, "curve", [(100, 280), (200, 280), (250, 200)])