You need a micro controller, GPS receiver, GSM module, and a SIM card.
You parse the incoming data from the GPS in the microcontroller. At whichever interval you program, you then have the microcontroller send data via AT+ commands to the GSM module to dial a number and send a formatted text message. You can give the location via internet, but I believe this to be a good bit more difficult than sending a text message.
As Nigel said -- it is not "easy" or "simple."