turn on headset
go to accessory settings > audio device settings
choose the headset as your input and output devices and test it's working .
some games have in game headset setup required also . read the games manual or check game options
some games require a button press to speak , other require you to adjust voip settings in the online lobby , others you have to choose to use voice chat when you create a game etc. so in some games the host will have to choose headset use or you won't be able to use one , etc.