The Earth (also known by smart asses as Terra) is an incredibly hoopy place to be, if for no other reason than because we don't know of any other place to be. Although many people have suggested going into outer space, and living there, more people have complained about everything that would entail, such as the longer commute to work or school, atrophied limbs in near-zero gravity, cramped quarters among spacecraft, horrible in-flight food and movies, and, of course, the amazingly large cost of sending a person anywhere outside the Earth.
The fact that we haven't left the Earth for any amount of time really hasn't upset anyone, though, since Earth is the only place where one can find a considerable number of video game machines, nice beaches, jobs, and members of the opposite sex. It is also the home of that wholly remarkable book, The Hitchhiker's Guide to the Galaxy, and its four sequels, all written by a certain human named Douglas Adams, and was, in fact, the sole inspiration for another wholly remarkable creation, Project Galactic Guide, the result of which you are now perusing.
For some truly outstanding figures about the planet Earth, you may wish to consult a recently published world almanac, which will give very interesting tidbits of information about the Earth, such as its size (approximately 24,900 miles around, with a surface area of 196,938,800 square miles), its moons (one, commonly called The Moon, but many smart asses call it Luna), and other things like the fact that Julia Child was born in Pasadena, California, on August 15th, 1912, and that, in 1987, the tallest building in Des Moines, Iowa, was the Ruan Center, which stood at an entirely uncolossal 457 feet tall.
The Earth is the only place we know of to date that has intelligent life living on it. This could, of course, be because of some global government cover-up (very likely), truth (least likely), or just because many people seem to be very troubled about the idea that there might be other creatures in outer space, and particularly that those creatures are probably more intelligent and evolved than they are (more likely than the cover-up idea, which was very likely, and thus is probably true).
The Earth is the third planet is the Sol star system, although the inhabitants are more likely to call Sol, their sun, The Sun, most likely because very few people have figured out exactly how to pronounce "Sol," but even more likely because they rarely talk about other suns, except as stars.
The Earth rotates on an axis at an angle, and orbits Sol in an elliptical orbit, the result of which is that the inhabitants feel different seasons, where, depending on their exact location, the average temperature will dip or rise, and various department stores will hold something called "Sales Events" as a form of acknowledgement to the passage of time. The Earth rotates on its axis once every 24 hours, and spends 365.25 sets of 24 hours (each set is called a day) in orbit, before reaching its original point, which isn't wholly true, as it is well known that the entire Sol star system is moving through space at an uncomfortable velocity, so uncomfortable that most people tend not to think about it, and, as a result, are not usually affected by it.
And to dismay any contrary opinion, to human conception, the Earth is indeed spheroidal, though not a perfect sphere in and of itself. Why this is is not important to most hitchhikers, however, and is left to brainy types, who have nothing better to do than to calculate the dimensions of our planet.
If you have any more questions, consult almost every other part of the Guide, or ask the nearest human, as they'll most likely know a little bit about the Earth (unless you're somewhere other than the Earth, in which case, if you do in fact find a human, they will be less likely able to tell you about the Earth).