One is the result of the other.
Get dressed = Action of putting your clothes on (getting dressed is the opposite of taking your clothes off)
Be dressed = State of having clothes on( being dressed is the opposite of being naked)
Your friend messages you early in the morning and invites you out for breakfast - you're still in your pyjamas. You message back and say 'OK, I just need to get dressed'. You put on your shirt, trousers, shoes etc and then message back 'Right, I'm dressed now', I'll be there in a minute'.
Likewise, 'get drunk' is the action of drinking alcohol - maybe sharing some beers with your friends in the pub.
'Be drunk' is the result - maybe when it's time to go home and you realise that you can't walk in a straight line. You sensibly decide to leave your car where it is and take a taxi home.