It is normal not to know things as programmers
The volunteers can't help you if we don't know you are lost
Someone else in the class probably has the same question as you, and is too scared to ask
If the teacher asks if everyone understands, SPEAK UP if you are not sure about something
Completion of all exercises is not success... if you do not truly understand.
If you learn so that you can complete any future exercises without help (e.g. in a job interview), that is success.
Each exercise is an opportunity to learn - don't let anyone steal that from you by solving your problem. Completing the exercise without understanding is a waste of your time and ours.
If you've done something in group-work that you don't fully understand:
Slow things down
Get it explained
Go back to the work by yourself afterwards, and challenge yourself to understand it
Don't let it go because the next time you don't understand something, it will be harder to get things explained.
So if you solve 10 exercises together in a group-work exercise, it is a great idea to go back over and try to solve them on your own the next day.
At a minimum, take note of the exercise numbers that you have problems with, even if you solve them eventually. Then you should revisit them some time afterwards and complete them again from scratch until you're positive you understand.
With simple programming challenges, it is easy to just repeatedly modify and re-run your program until it works, but you won't learn much unless you are thinking (and this playful approach doesn't work with more complicated problems), so instead...
Always try to predict what your code will do before you run it. Write your prediction down, or tell your a friend - you can make it a game. After you run the program, if your guess was wrong, discuss why, then FIND OUT why.
The instructors have told them not to! Can you say why?