How do I tell my employers about all the holidays?

I’m a student and I just got an internship for the fall semester with the first day on august 30th. I’m getting really nervous about how to let my boss, whom I have yet to meet, that I will have to take off 7 days during the month of September. I know I’ll have to tell them the first day because that’s only a week before rosh hashana and I’m really nervous because that is an awful way to make a first impression. How do I handle this? In school I just tell the professors that I’ll make up the work and they don’t really care but this feels a little different. Thanks in advance!