You don't need childbirth classes. Your body knows how to give birth, if you're just allowed some freedom and some privacy in labour to relax and do what feels right.
Just try to remember: you are a mammal and give birth like a mammal.
Mooing, lowing, groaning, sighing.... swaying your body, being with someone who makes you feel safe, relaxing and not fighting the overwhelming bodily sensations (especially not the one that feels like you need to have the biggest crap in the world, but is actually your baby pressing against your back passage as he or she is being born).
Avoiding too much talking, contact with strangers, bright lights, interference and intellectual stimulation,
Breathing: keep it deep, keep it slow, keep it going.
If you think along those lines you can't go far wrong.