Composite glyphs
Composite glyphs are made of other glyphs. On the left you see the glyph and on the right you see one of the used glyphs. You can change the position of each of the used glyphs as well as the scale and rotation.

Warning: avoid recursively using the composite glyph your are editing as this will result in a brute faillure of the program! Try it once (but first save your fonts) and you won't forget it about this warning.
Tip: you can zoom out the left image by right-clicking on it. Now you can select another zoom factor.
Next: Import an image...