XBMC System Settings Menu
XBMC Settings Add-Ons
XBMC Add-Ons Get Add-Ons
Open up XBMC, highlight the “System” menu, and select Settings. Now click on the Add-ons entry, then Get Add-ons.

XBMC Add-Ons Repositories
You should see various repos listed – please select the one you want to check out and then navigate around the repo.

XBMC Add-Ons Repo Video Add-Ons
XBMC Select Add-On To Install
XBMC Add-On Install Button
Different repositories have different file/folder structures, but once you’ve found the add-on you want to install (for example, from within the Video Add-ons menu), select it, then click the Install button.
Once the process has completed, restart XBMC (using the power/shutdown icon found on XBMC’s homescreen, next to the little star).

XBMC Video Add-Ons
Now when you open the Videos>Add-Ons menu, the new add-on should be present.

XBMC Add-Ons Configure
If you want to configure it before using the add-on, highlight the entry and click C if you have a QWERTY keyboard, or otherwise the Menu key on your remote control, then select Add-on settings.