How do I track my iPhone using Find My?

See how here --> Find your lost iPhone or iPad - Apple Support

You can track your phone using Find My if you had Find My enabled on the phone before your phone was lost, or stolen, and if your phone is able to report its location (e.g., is turned on, has battery power, and a Wi-Fi or cellular Internet connection).

Find your lost iPhone or iPad - Apple Support

If your phone was stolen, do not go to any location that you might see to confront criminals in person. You might lose a lot more than just a phone.