1 Read these documents:
User Guide ...\doc\sklanguser\sklanguser.pdf
SKILL API ...\doc\algroskill\algroskill.pdf
SKILL (Lisp) Reference ...\doc\sklangref\sklangref.pdf
2 Review examples ...\share\pcb\examples\skill\
3 Read forum, it contains docs on Chines.
4 Think up simple task as exercise. Resolve it.
....
PROFIT
PS For debugging use console in PCB Editor.
Inter "skill" command, that switch console to SKILL mode. ("exit" for return to command mode)
Now, step-by-step print operators from your SKILL program and view result immediately.