From The Battle for Wesnoth Wiki
This section of the tutorial will help you install the skeleton campaign, and customize it to make it your own.
Installing The Campaign
To install the skeleton campaign, follow the following instructions:
- Download the campaign (link).
- Unzip the downloaded file.
- Move the newly unzipped folder (entitled "A_Simple_Campaign") into the following directory: "(userdata)/data/campaigns". Once it's moved, the campaign directory should be located at "(userdata)/data/campaigns/A_Simple_Campaign".
- Run Wesnoth
- From the main screen, click "Campaign". Scroll down until you find a campaign called "A Simple Campaign". Select it, select a difficulty, and make sure that the first scenario loads. If everything works correctly, then move on to the next section. If at any point you get an error message, or the campaign doesn't appear in the list at all, then make sure that you performed each of the steps above correctly. If you did, and the problem persists, leave a comment on the forum post.