Ground control stations are located all around the globe. To tell an unmanned spacecraft what to do, controllers send coded radio signals to the satellite and receive similar signals from it. For instance, a newly-orbiting satellite can be told to unfold its electrical solar panels and communication antennas and turn on science instruments.
Ground controllers can instruct an observation satellite to look elsewhere.
A weather satellite might be told to stare at a hurricane. The radio frequency used by a communications satellite to beam down a TV movie can be changed. A spysat can be ordered to modify its orbit to fly its sensors over specific ground targets. NASA controls its constellation of TDRS communication satellites from a ground station in White Sands, New Mexico. Many military satellites are operated from ground control stations in Colorado and California.