Area 51

It's an extremely secretive workplace. Everyone signs very strict confidentiality agreements. They can't talk about what they do, not even to their families. The pace is that of a high-level testing facility: technical, disciplined, and highly controlled.
There is no official evidence of extraterrestrial activity. What is confirmed is that it is a testing center for advanced military aeronautical technology (from the U-2 and SR-71 in the past to more modern stealth aircraft and drones today).

The people who work there (test pilots, engineers, technicians, maintenance and security personnel) are mainly engaged in testing and development of experimental aircraft and advanced military systems.
Typical activities (according to what is officially and declassified known):
Flight tests: Test pilots take prototype or modified aircraft to the runways, conduct evaluation flights (speed, stealth, sensors, weaponry, etc.), and land them again. Many tests are done at night for greater secrecy.
Engineering and maintenance work: Technicians and engineers inspect, modify, repair, or prepare aircraft in the hangars. They analyze data from previous flights and prepare for upcoming tests.
Data analysis and development: Test results are studied, designs are adjusted, and new technologies are developed (stealth aircraft, drones, radar systems, etc.).
Logistics and support: Personnel who maintain the runways, special fuel, communication systems, perimeter security and basic facilities (dining room, accommodations, etc.).
Daily transportation: Most personnel do not live on base. They arrive in the morning on Janet aircraft (from Las Vegas) and leave in the afternoon. Some stay for several days or weeks depending on the project.

For decades the government denied or did not confirm its existence, which generated a lot of conspiracy theories: that extraterrestrial spacecraft are kept there, aliens are studied there, UFO technology is reverse-engineered there, etc. These ideas became especially popular from the 80s and 90s onwards with testimonies from alleged former employees and pop culture (movies, series, the internet).
In 2013, the CIA declassified documents officially acknowledging the existence of the base and its role in the U-2 program. Even so, it remains an extremely heavily guarded place: public access is prohibited, there are signs of “authorized use of lethal force,” and it is constantly monitored.

Its confirmed use is the development and testing of experimental aircraft and advanced weapons systems. It was built in 1955 (initially called “Paradise Ranch” or “Dreamland”) to test the CIA's U-2 spy plane. Later, it was used for other secret projects such as the A-12 Oxcart, the SR-71 Blackbird, and stealth aircraft. Today, it remains a restricted military testing and training area.

Area 51 (also known as Groom Lake or Homey Airport) is a highly classified United States Air Force military installation located in the southern Nevada desert, about 130-135 km northwest of Las Vegas.
It is part of the Nevada Test and Training Range and is administered by Edwards Air Force Base. Its official name is usually Homey Airport (ICAO code: KXTA) or Groom Lake (for the dry lakebed next to its runway). The name “Area 51” comes from a designation on Atomic Energy Commission maps.