If you want to install addons for Warhammer, you'll need to create a folder inside your warhammer folder. So open it now. When you're inside your warhammer folder, create a new one called Interface. Inside that one, create another called AddOns. You'll be installing all your addons in this last one.

Now go to http://war.curse.com and click on the Addons section. Manually download any ones you want to try and unzip them. When unzipped, you'll get a folder called something like "Blablabla version 2.03". Open it and you'll find a folder simply called something like "Blablabla". That's the folder you must copy into your Interface\AddOns folder you created in your warhammer folder.

Remember you can move anything around on your screen using Customize Interface options in WAR.

IMPORTANT : THERE IS ONE ADDON THAT EVERYONE NEEDS TO RUN OTHER ADDONS, IT'S CALLED LIBSLASH. Get it from the war.curse.com website.