Eclipses happen all the time. It just depends on where you are at the time. Here on earth, we've got the best ones in the solar system.
The eclipse on July 22 is a total solar eclipse, so named because the moon will totally obscure the sun's bright disk as viewed from here on earth. It will the longest one of this century, not to be surpassed until 2132.
Solar eclipses can only occur during a new moon, when the perpetually dark side of earth's satellite (as seen from earth) is facing us, and also only on those rare occasions when the sun, moon and earth's orbits are in the proper alignment at appropriate distances. This happens on average slightly more than twice a year.