This could be a silly question to ask, but I would like to know why is a gibbous moon shape possible.
From the few cases I've drawn here, I could not think of a configuration where the Earth's shadow can be cast on the Moon in a way that leads to a gibbous shape of the bright part of Moon. In my diagrams, grey represents bright and black represents shadowed portions of the Moon (smaller circles, with the bigger circles being Earth).
As for the order of the celestial bodies, the Sun is out of the screen, Earth is on the screen and the Moon is inside the screen. That could be a crude arrangement but it's the only one I can come up with to cast shadows, though I can accept the fact that there could be more complex 3-D arrangements.