Here is an example session with AKCL.  I have edited in some comments
which appear after the `;' character, as they do in Lisp source code.
						
gizmo(41):~/lisp/akcl.project/newport/temp> saved_kcl	; how to start Lisp

AKCL (Austin Kyoto Common Lisp)  Version(1.615) Tue Aug 10 14:22:35 EDT 1993
Contains Enhancements by W. Schelter

>(load "fact.lisp")			; how to load a Lisp program 
Loading fact.lisp
Finished loading fact.lisp
T

>(fact 4)				; 4! = 24
24

>(fact 300)				; 300! is bigger...	
306057512216440636035370461297268629388588804173576999416776741259476533176716867465515291422477573349939147888701726368864263907759003154226842927906974559841225476930271954604008012215776252176854255965356903506788725264321896264299365204576448830388909753943489625436053225980776521270822437639449120128678675368305712293681943649956460498166450227716500185176546469340112226034729724066333258583506870150169794168850353752137554910289126407157154830282284937952636580145235233156936482233436799254594095276820608062232812387383880817049600000000000000000000000000000000000000000000000000000000000000000000000000

>(fact 340)				; Doubling IHSSIZE in frame.h
					; lets us get (fact 680)
Error: Invocation history stack overflow.
Fast links are on: do (use-fast-links nil) for debugging
Error signalled by FACT.
Broken at FACT.  Type :H for Help.
>>:q					; how to get out of the debugger

Top level.
>(bye)					; how to leave Lisp
Bye.
gizmo(42):~/lisp/akcl.project/newport/temp> 

Please see the KCL docs for a much better explanation...