GPS

All iPhone have builtin aGPS.

There is no installation needed, make sure your cellular data is provision properly and your Wi-Fi is working.

If you have a specific needs. you might need to get an app.

It does and it is built in. Some features that use GPS need to be turned on in order for them to work. For example: Set up Find My iPhone on all of your devices - Apple Support

Yes.

Turn Location Services and GPS on or off on your iPhone, iPad, or iPod touch - Apple Support