I found your question while searching for the answer myself; eventually I hit upon this video that shows it in use: https://www.youtube.com/watch?v=JcOCNgXXhmE
Basically, you have to set a breakpoint in a file you're editing, import the file in the console, click the "Attach Debugger" button and then run code that hits the breakpoint -- at that point, the debugger tool will open and you can step through it.
It's not exactly what I was hoping for -- I was hoping to attach the debugger and then step through a statement I'd just typed, as one can with IPython's %debug <statement>
(which still works, but does not provide the visual niceties).
The best solution I've found for that is to use a scratch file, type the statement I want to step through, then run the debugger with that.
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