Your questions doesn't really make sense as is.
You would buy a GPS module and its reliability and accuracy would depend on which one. Discussed here and on other forums many times.
Most GPS modules have a serial data output that almost any u-controller, processor or even a PC can receive. You write code in any language supported by the development tools for that processor to receive and decode the GPS serial data.
Again, discussed many times in forums.
Start with searching the SoR forum for GPS. Then google search and read Wiki on GPS.