What is exactly a Global Positioning System (GPS)?

It is a satellit based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. At first, GPS was going to be used by military applications, but later in the 1980s, the government allowed it to be available for civilian use. It doesn't matter the weather conditions, GPS keeps working anywhere in the world and the whole day. It is not necessary any subscription fees or setup charges to use GPS.

The second question would be: How it works?

GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers can calculate exactly where the user is by taking this information and using triangulation. In other words, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. And by repeating this procedure with a few more satellites, the receiver can determine the user's position and show it on the unit's electronic map.

A GPS receiver can calculate the latitude and longitude and track movement if it is locked on to the signal of at least three satellites. And it can determine the user's latitude, longitude and altitude using four or more satellites. But it doesn't end with this, because once we have the user's position, the GPS unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, and much more. So not just you can know where exactly somebody is, but also you can know a lot of things about that person, and it doesn't matter where in the world that person may be.