Twenty Eleven theme question

I am brand new to blogging (two days into it). I am using the Twenty Eleven theme on my blog. So far I don’t have much content, but am messing around, trying to figure things out.

My question: just under the header, there is a black bar. When I add a new page, it automatically goes in that bar… And I don’t necessarily want ALL of my pages there. How do I control what does and what does not go on that bar?

Thank you!
Sarah