Find my iPhone works with iCloud and your GPS (or if you haven't signed up for icloud with the appleid that uyou used to set up find my iPhone). If you go to icloud.com and log in with the apple id that you used to sign up with on your phone, you will be able to click on find my iPhone. Type your password in again and your device will appear in the sidebar if it is online. Click on it to view it's location and press the i next to the phone's name on the map to see options for remote lock or wipe, or for sending a a message/sound.