How to save files in subfolders?

Example: I'm saving an email and get the dialog box asking me where to save it. I can choose Documents, but can't choose subfile (client correspondence which is nested within the Documents folder a few levels down.) So I have to save to Documents, then go in later and move it.

Thanks for any help! I'm a life-long Mac person, and this was easily done in OS 9, but haven't figured out how to do this in OS X yet...and it doesn't seem to be covered in the support/Mac 101 info.

Leslie