It has less to do with being "quiet" than with interrupting the person next to you and making it impossible for her to hear what the instructor has to say. When I've paid good $$$ for a class, I don't want to miss a single minute of it.
If you don't understand what the teacher is saying, please raise you hand and ask her directly. She may answer your question right away especially if others are nodding their heads; or if it's obvious you're in over your head, she may tell you she'll come help you with she finishes with that step.
Please make sure when you take a class that you understand how to sew with your machine and how to do basic quilting. When you sign up for a class at our LQS, the class is rated "Beginner" "Intermediate" "Advanced": if you're not sure, ask the shop owner if the class is right for you. If you've been taking other classes or BOMs, she'll either know your quilting expertise or she'll know the correct questions to ask you to advise you.
At the same time, don't be afraid to stretch your wings.
Bottom line: don't ask questions of the person next to you in the middle of instruction. Please.
Retreats: each one is different.
Read the notice that was sent out and if you have questions about how it works, ask! Some retreats are very chit-chatty and some aren't. You should also ask if everyone brings treats to share; or a little something to give to everyone else (example: an ort bag): you don't want to be embarrassed by being the only one treat-less or present-less.