To track a lost iPhone using GPS, first you need to activate "Find my iPhone" in the settings menu. Then, if the phone becomes lost, log into the iCloud website or use a Find my iPhone app on another connected device to see a map of the phone's current location.
In addition to tracking a lost or stolen iPhone, the iCloud website offers many features that may help reunite a user with his device or at least minimize the damage due to stolen data. iCloud allows a user to log into his missing device and play sounds or put messages on the screen to inform finders where to return the device. In the case of a stolen iPhone, a user can also lock the device to prevent unauthorized use or wipe all personal data. Since these tools can be used by anyone with access to the iCloud account, users should ensure that the passwords securing their accounts are not difficult to crack.
When an iPhone is in lost mode, it reports its current location any time it has a Wi-Fi or cellular signal. The user can view a map of its current or most recent location and even touch an icon to bring up driving directions to the spot.