do i have to add hey when talking to siri?

If you invoke Siri with the side button, no; just hold the side button and speak your request. But if you want Siri to respond to a voice request then you must say “Hey, Siri” followed by your request. You don’t have to pause in either case; for example, “Hey Siri, what is tomorrows weather?"

If you have an Watch, just lift your wrist to your face and speak your request; no need to say “hey siri” and no need to pause. In fact, if you DO pause, Siri won’t be activated; the watch will assume you just want to look at the time.