In that case you are returning a reference to an ostream object. Strictly thinking of ampersand as “address of” will not always work for you. Here’s some info from C++ FAQ Lite on references.
As far as const goes, const correctness is very important in C++ type safety and something you’ll want to do as much as you can. Another page from the FAQ helps in that regard. const helps you from side effect-related changes mucking up your data in situations where you might not expect it.