what is the difference between non exempt and exempt workers?
That depends.
If your employer has established an alternate work week under CA regs, you are not entitled to overtime since you are working 4 10 hour days and not going over 40 hours in a week.
If your employer has not established an alternate work week under CA regs, you are entitled to overtime because you are working more than 8 hours in a day.
Forget exempt and non-exempt for now. The percentage of exempt employees who can legally be paid on an hourly basis is so small it's not worth the bother. Unless you are doing something very, very high up in computers, if you're being paid hourly for a shipping company you're non-exempt.
Don't ask us if your employer has established an alternate work week. There is no possible way for us to know that for certain. It can be assumed that they have, because if they're having you work 4 10 hour days they'd be idiots not to have, but the only way to tell FOR SURE is to ask them.