I was wondering how do you use find my iPhone?
Log into https://www.icloud.com using the same appleid used for iCloud on the phone. Click the Find my iPhone Button.

You can also use the Find iPhone app on someone else phone.  Just log into that app (it opens to the login screen) using your appleid and password as above.

You can also "play sound" (even if the device is on vibrate only), set lost mode, and remote wipe the device.   FWIW, you don't really want to remote wipe a lost/stolen, just set lost mode so the phone remains trackable, once it's wiped it's no longer trackable.