First thing you do when the radio breaks down is to start squawking 7600 (the code for radio malfunction) on your transponder.
Then when you approach the airport they will attempt to contact you first through radio (to see if you can still hear them) and you use alternate means of replying (sending IDENT on transponder, rocking your wings,...).
If you can't hear them they will use a light gun to convey messages.