You will need the PokeMon Go app: Grab it here
You also need the Fly GPS app: Grab it here
-On your phone head to settings, about phone, click build number 7 times to unlock developer options.
-Open developer options, choose mock location, choose Fly GPS
-Go to location settings, be sure high accuracy is turned on and location history is turned on (WARNING THIS MOD MAY GET YOU BANNED) (How To Avoid A Permanent Ban!) although i have had pretty good luck with it.
-Open Fly GPS, choose your location, tap the text box to bring up options, run fly gps, run pokemon joystick
-Open Pokemon Go