[slime-devel] how do I invoke the debugger and step through a function?

I've created a function (defun tester () ...) that does almost what I want - but its not totally correct. I would like to use the slime debugger to start this function and single step through its various parts to see where the mistake is. How do I do that with slime? I am using slime-1.0 and cmucl-19a. Thanks for any help. -Ram