how to use the step ?

[ctu]

hello,

how to use the "step" in cmucl ? it invokes the debugger, but then how to go 
further ? the u,d ... don't help me much :-(

examples to step :

* (step (+ 1 (+ 2 3)))

* (step (DEFCLASS TOTO NIL ((X :ACCESSOR GS-X))))


ctu.