thanks everyone for helping me out!
I managed to editing the class, and already created the new skill, following the tutorial http://rathena.org/wiki/Adding_new_skills,
in fact i finished the tutorial, both server and client side, and on my client i can see the skill but i cant "buy" the skill
any leads?
EDIT: if i use the command: @useskill 8443 10 "char name" it casts on me and on chat appears: skill has failed(i think is normal, the skill is like firebolt)
i found this thread http://rathena.org/board/topic/64654-src-custom-skill/, but still without answer
edit 2: the skill is working perfectly with @useskill and targeting other player on pvp. I just dont now why I cant "buy" the skill on the skill tree.