From the "Help" menu, go to "What's New In Max 5?", scroll down to the section "Debugging and Monitoring", then click on the link for "Debug Window" and there should be an explanation as well as a few instructions. Albeit, not the best place to search for the info. about it, but hopefully it can give you a start.
The Debug Panel is for the internal use of Max developers only and the menu item will be removed from the Debug menu for future releases. If its presence is bothersome, merely remove it from the menu item list in maxinterface.json.
ah, looks like David cleared it up.
also, i was confusing the debugger with the debug panel(debugger pulls up debug window, whereas the debug panel is the internal/developer used interface for other things...)
also, on macosx max5.0.4 if you click on the help menu, there is a search engine just above the help entries, "help, reference, and query" but now i see that the debug panel that shows up is not a help doc but the actual panel. sorry for all the confusion.