I'm sure we all know the intent of Mr. Geezer's answer, but, perhaps pedantically, the Moon is always between the Earth and Sun distance wise. To expand slightly on Geezer's offering, a solar eclipse occurs when the Moon is positioned to cast a shadow on a portion of Earth. Since the Moon circles the Earth the shadow is moving as it crosses a swath of the Earth...
Additionally, since the Moon revoves around the Earth once a month we would intuitively expect there to be a solar eclipse once each 30 days or so. However, the Moon's orbit is about 5 degrees out of the plane of the Sun's equator referencing Earth's orbit dictating a full solar eclipse to be a rarity.
Finally, Lunar Eclipses also occur..."when the full Moon passes through the shadow of the Earth. In this case, the Sun and the Moon are on opposite sides of the Earth. If you observe a lunar eclipse (visible only at night at the time of certain full Moons), you�ll see the bright lunar disk turn dark -- sometimes a coppery red color -- for as long as an hour or more...".