[slime-devel] basic sldb question

I am teaching myself lisp, but sometimes I like to step through other people's code using a debugger. I'm trying to figure out how the sldb debugger works in slime, but I am having trouble doing so. The documentation here: http://common-lisp.net/project/slime/doc/html/Examining-frames.html#Examinin... talks about "frames". Ummm, what's a frame? How do I stop execution of code in slime/emacs and run each line one by one? I checked documentation and I searched around in google, but strangely enough I can't find much on it. - Steve