The feature is available on iPhone and Android Facebook apps, and it can be easily turned on or off. If you turn on Nearby Friends, you’ll occasionally be notified when friends are nearby, so you can get in touch with them and meet up.
The feature uses a smartphone’s GPS system to tell its location – provided that the user has turned the “Nearby Feature” on, on his/her smartphone.
It’s also located under the “More” category on the tabs on the bottom of your application, close to Nearby Places if you don’t see it in your News Feed. From here you also can easily click “Turn On” to enable the feature.