It's a difficult one. In a traditional setting where you aren't being judged or examined constantly it's easier to enforce behaviour (spending lessons just waiting for silence, detention after detention).

You could try and build rapport with students, find some common ground. Get the head of year, assistant head teacher in and get them told. Unfortunately some schools are like this and the teachers become oblivious as time goes on and just let it slide.

Speak with your university lecturer or training provider.

Not every school is like that. It's easier said than believed? If that's the right was to say it... But honestly hang in there. Behaviour management is 90% of ensuring pupils make progress Imo.

Good luck