How do I use Find My to locate my iPhone?

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.

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

iPhone User Guide - Apple Support (CA)

Start reading the guide and keep it handy

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.