First Addon - need help

[opismahname]

Hey there, I'm making my first AddOn that will be a real simple one. The thing i want this AddOn to do is to print "Rigtheous Fury is now activated" in the chat window when you cast Righteous Fury.

I've been reading alot about how to do something like this but still can't get it...

The code I am doing is like this (i know, i suck at this, but it's like my first time):

local frame = CreateFrame("FRAME", "RFFrame");
frame:RegisterEvent("UNIT_AURA_PLAYER_RIGHTEOUS FURY");
local function eventHandler(self, event, ...)
 print("Rigtheous Fury is now activated " .. event);
end
frame:SetScript("OnEvent", eventHandler);

I know that this isn't right at all, but don't know what to do

Really need help...