Rush Question

My mother and I are going to NY in two weeks and would like to see Legally Blonde. Neither of us has ever been to a Broadway show before (We've seen touring performances though). I'm a student and found out about student rush, which I'd like to try. I've searched this board and a few other places online but I can't find where exactly I'd have to go to purchase these type of tickets. I keep finding 'buy them at the box office' at the day of the show and get there early, but no where does any place tell me where this elusive box office is. Is there one big office where you can buy rush tickets to any show that offers them, or do I have to go to the theatre where the show I want to see is being performed?

Any help you can offer this newbie would be greatly appreciated.

If it hasn't been made clear, the box office is in the theatre.

The Box office typically opens at 10 o'clock am.