Board Thread:General Discussion/@comment-233706-20150624014033/@comment-1277243-20150624021023

Depending on the options selected, Special:Export will either select the latest revision or all revisions of the selected pages and place all the text in an XML file, which Special:Import can read. It doesn't do images, but there are separate tools to import those. Depending on how big the wiki is, you may have to split the pages up into a couple batches.

As to how there can be more than one wiki about the same subject, it's because Wikia allows there to be. Just look at Special:NewWikis to see all the new wikis that are created that probably already have a wiki for that subject.