Earth is but one planet in a our solar system. Our solar system has 8 planets--Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune--since Pluto is no longer a planet. Thanks stupid scientists and your anal criteria. There are loads of asteroids, comets, etc. too. Of our 8 planets, 6 of them have moons--one for Earth, two for Mars, 63 for Jupiter, 60 for Saturn, 27 for Uranus, and 13 for Neptune. Our Solar System has one sun.
Our sun is a star in the Milky Way Galaxy. There are billions upon billions of other starts in our galaxy, and millions of them are similar to our sun. There are hundreds of confirmed exo-planets--planets around other stars. Our galaxy is one of billions of other galaxies in our universe. In those galaxies there are billions upon billions of other stars, and since the Universe is so vast, this means there are so many stars and so many chances for life out there, that the thought that we would have been only intelligent life to emerge is absurd. (Note that we probably will never see those other lifeforms).
Now, here is where things get even more ridiculous in regards to our insignificance. Scientists are theorizing that our universe is not the only one out there. Now this could mean that maybe there are just many universes that act as big bubbles in the vastness of space, sort of like galaxies are in our universe, or it could mean that alternate dimensions are at work. This all sounds very crazy, but there is some real strength to the theories, most particularly the whole deal with the ten dimensions.
So how's that for putting things into perspective?