my phone is stolen, how do i track it?

These are the only steps you can perform in such a situation:--> Use the Find My app to locate a missing device or item - Apple Support

and/or these:--> If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

Regards

Giulio

You should do more than just track it,

Here's the list of things you need to do, including how to track your iPhone with Find My (As long as you didn't disable it)

https://support.apple.com/en-gb/HT201472

In order for you to track it the phone has to be on, not wiped, and able to connect to a network: if any of these isn't true you can't ntrack it, though you should still follow the advice outlined in the two posts above. A half-competent thief may well tey to erase or otherwise disable the phone.

In the event that you are actually able to locate it you should not attempt to retrieve it yourself - that could be dangerous. Report it to the Police who may be able to retrieve it.