The Sun is a star that represents the center of our Galaxy. The Earth orbits around the sun and one "circle" around it is called a year. The Earth revolves around an imaginary axis and completes one circle in 24 hours. This is what causes day and night - one side of the Earth is facing the sun - so it's light, and the other doesn't - so it's dark. The sun lights the moon and that is why at night we see the moon. The sun radiates energy and warms up the Earth. Without that energy the life on our planet will not be possible.
The Moon is Earth's natural satellite and it revolves around the Earth, like the Sun revolves around the Sun. The Moon has a gravitational pull that causes a rise and fall of ocean tides.
