I suggest Wikipedia's article:

https://en.wikipedia.org/wiki/Area_51

"The base's current primary purpose is publicly unknown; however, based on historical evidence, it most likely supports development and testing of experimental aircraft and weapons systems. The intense secrecy surrounding the base has made it the frequent subject of conspiracy theories and a central component to unidentified flying object (UFO) folklore."

According to news reports, aeclassified documents have confirmed that Area 51 was <em>definitely</em> used for testing the U2 spy plane.

I know is a place in desert when it used to criated the false arrived from man in the moon, it's impossible the human live at moon.  it's a military base.

No, it exists. It's just that there are a lot of false conspiracy theories about it. 

It doesn't exist

I once watched a documentary about Area 51. As far as I remember, it was mostly used for testing new (espionage) aircrafts. They put up an aircraft, covered in the first stealth-coating, on top of a large pole. They'd use their radars to look if the plain would be visible or not, to perfectionate the stealth. I'm not sure what they're doing at the moment, guess that's "classified information".