How do you make an Addon?

Does anyone know where i can find a guide on how to make an addon?

I'd suggest looking at the UI section on WoWwiki, or, if you're looking for something more friendly, pick up a copy of the "Hacking World of Warcraft" book (which, in spite of the name, is about addons, making addons, and making macros, not about hacks/cheats).

I actually suggest finding an addon similar to the one you want to make if you are just starting out, and use some of the code to get started.

Here is an addon someone made so people can edit it to get started: (AddonTemplate)
http://www.curse.com/downloads/details/3462/

Here are some functions that wow uses:
http://www.wowwiki.com/World_of_Warcraft_API

Here is a link for a bunch of HOWTO on WoWWiki:
http://www.wowwiki.com/Category:HOWTOs

Getting started link with the basics:
http://www.wowwiki.com/HOWTO:_Get_Started

About Handling EVENTS:
http://www.wowwiki.com/Events_(API)

Information on lua strings:
http://lua-users.org/wiki/StringLibraryTutorial

Patterns of strings in lua:
http://lua-users.org/wiki/PatternsTutorial
http://www.wowwiki.com/Patterns_fired_from_each_CHAT_MSG_events#CHAT_MSG_LOOT

If all else fails make a macro:
http://forums.worldofwarcraft.com/thread.html?topicId=96143900&sid=1

Hope this helps
-Necro