GPS is short name used for the term Global Positioning System. A Mobile Handset with GPS functionality can be used to track position. GPS hardware in mobile provides physical co-ordinates (in terms of latitude and longitude) to the operating system of the mobile and an appropriate application installed in the mobile displays the latitude and longitude information on map.
In case you do have a GPS mobile handset, all you need is appropriate software and maps of your country to see your current position on maps. There are various companies which provides maps of various countries. Google Maps is one of the well known web based map application providing maps of almost all countries on the earth, OVI Maps is another web based map system, Nokia Maps is another sophisticated map provider for Nokia mobiles, MapMyIndia is another map provider for Indian cities.
TomTom is a physical device popular in UK and European countries specifically made to display current physical location and provide voice assisted map navigation. As TomTom has been made specifically for providing navigation capabilities, it is really sophisticated system providing voice control navigation (such as after 10 yards turn left, make a right turn now, etc).
The GPS functionality is free to use for everybody provided you have the required hardware and appropriate maps of the desired country. In case you have bought / planning to buy a Nokia Mobile with GPS functionality, all you would need is to get the appropriate maps and you are ready to navigate to any place with your maps.