NASA, or National Aeronautics and Space Administration in full, is a US governmental agency that studies outer space, astronautics and aeronautics.
NASA created several generations of rockets as well as the Space Shuttle. In the 1960s, it launched the Apollo Program, a program which sent several capsules into space and was the first mission which put men on the Moon. Together with other space agencies, it built and operates the International Space Station used by scientists to better understand various aspects of life in general, human health, materials and more. NASA also launched several remote sensing satellites for Earth observation: these are used to monitor ecosystems and land cover, identify human impact (positive and negative) on the environment, plan land use, etc.
All this has a significant cost: over the last 40 years, approximately 1% of American taxpayers' money went to NASA. In 2012, NASA had a budget of 18.7 billion dollars, slightly over half a percent of the entire U.S. budget.