Atlas
You will probably find Atlas to be a crucial map mod that really should have been part of the game in the first place. For some curious reason, Blizzard doesn't have the instances mapped in Azeroth. Fortunately, Atlas solves this problem. It adds a map for every instance in World of Warcraft and it includes the boss locations too. There are also a variety of map pack plug-ins made for it so you can use those to add additional maps for things like dungeon locations, raid bosses (outdoors) and battlegrounds. This comes in extremely handy and you only have to install the ones that you need.
Cartographer
The Cartographer addon adds coordinates to Warcraft world map, but it also does a number of other cool things as well. You can use it to add notes, or change how the map looks with scale and transparency adjustments, etc. It also keeps track of herbs and minerals. In addition, it also shows unexplored locations on the map, which you may find pretty useful.
MobMap
Looking for lots of easy quest mobs? Then MobMap will prove indispensable. It adds the positions for all NPCs and the known mobs to your in-game map. MobMap also comes with quest and merchant databases. This map mod is also available in German.
QuestHelper
QuestHelper is another map mod that will help you out with questing. It adds all the waypoints for the quests in your quest log to your map and sorts them by shortest distance between quests in order to cut-down on how much walking you need to do between each quest. This will prove to be a real time saver.
MapMod v2 leveling addon
MapMod v2 is the only addon here that isn't free, but I'm including it because if you are interested in leveling fast, whether for Alliance or Horde, you are going to find it useful. It's made by the Team iDemise crew. Like Questhelper, it adds waypoints to the in-game map, but it does a lot more than that. It basically provides a leveling walk-through so you can just follow the arrows from one quest to the next. Also installed with it are step by step written instructions and hint and tips that are all accessible from both the Mini-map and the world map.
the only jeapordy addon found is linked below to the Curse addon site. It adds some sounds for certain events.
In general all you need for downloading and using an addon are WoW itself and a web-browser to download the addon from a third party site like wowinterface or curse. That said, there are addon-control packages like the curse client, which allow you to download and update many addons from a central program.
I would start by browsing the UI & Macros forum at the site in the related links. It is on the official wow forums and will give you a huge head-start in your addon development.
The best free leveling guide is actually an addon which tells you which quests you can do, and even gives you a map location on where to go. Examples of these addons are Carbonite and Quest Helper, both of which allow you to do quests quickly and efficiently. These addons can be found on well-known addon sites like Wowinterface or Curse.
No, most addons will not get you banned. The only things that addons are allowed to do in game are approved by Blizzard. If Blizzard does not want an addon to do something, they just make it so that addon can not do it.
You will need an addon in order to move the experience bar. It is not a thing that you can do with out one.
No - all WoW addons require registration ($) and the previous addon: WotlK requires The Burning Crusade, The Burning Crusade requires a registered version of WoW.
Button forge is an addon, you would be better off going to the addon authors help site if he has one, or the wow forums. They will be better able to help you.
Download the addon. You can usually find this on the Curse Addons website (listed in the links). Save it. Then move it to your addon folder in your World of Warcraft folder. To find the folder go to your wow folder, then interface, and inside that should be addons. Next time you are at the character screen an addon button will be on the lower left.
Download a wow addon manager like wowmatrix. Google Wowmatrix --- Inside your World of Warcraft game folder you will find a folder called "Interface". Inside is a folder called "Addons". Addons provided on abovementioned websites usually come zipped, with the files in a folder with the addon's name. Simply copy this folder entirely into the "Addons" folder. Make sure to quit WoW and restart it. At your character selection screen, at the bottom right, is a button "Addons". Click it to see a list of addons you are using. Make sure all addons you want to use have a tick in the box, and that the box "Load out of Date Addons" is ticked, in case you installed an older addon. Log into your character, and the addon should now be active.
You should download the curse client and download the addons via that, on my computer the addons automatically go to the WoW addons folder located in the interface section of the WoW folder.
In order to manually install an addon, first download the addon and unpack its zip file. Everything contained inside the zip file should then be copied into the World of Warcraft\Interface\Addons folder. When you start up World of Warcraft again, click the "addons" button at the bottom left of the character selection screen and make sure that the addon is there and the box in front of it is checked. The addon should now be running properly. If the addon has not been updated for some time, you may need to click the "load out of date addons" option for it to work, but this increases the chance of the addon causing errors.