I’ll need a little more information to get a handle on what you’re trying to do here. Are you trying to make a text box appear below the menu when you’re on a specific page? This isn’t really doable through WordPress because the Header is a global file which is referenced identical on every page using a php_getheader command. To have custom text you would need to input it in the body of each page where you want this text to appear.
If you’d like to provide some more details on what you’re trying to achieve, perhaps if you could show an example then I will see what I can do, though we might be restricted by the capabilities of wordpress on this one.