How do I use Find My to locate my iPhone?

Does Find My say the phone is "Offline", or the phone does not appear in the list at all?

If it doesn’t appear in the list at all, your only option is to retrace your steps and look for it the old fashioned way.

If it doesn't appear on your "find my" list of devices at all more than likely you did not have "find my" on before losing the device.

iPhone User Guide - Apple Support (CA)

Start reading the guide and keep it handy