Board Thread:Support Requests - Getting Started/@comment-26194056-20150327025353/@comment-4189499-20150327031417

There are 3 buttons which are showing themselves in the link editor in the VisualEditor (the default editor on Wikia): open, which opens the page you're trying to link to in a new tab to check that it is the correct link, remove, which removes the link from the text if that was how you entered the link editor, and OK, which confirms the link and places it on the article. If you can't see the OK button, then you should send in a Special:Contact with the URL of the page you can't see the button on.

Of course, you could just circumvent the whole VisualEditor mess by using the source editor (under the Classic Editor in the drop down menu beside the edit button). There you can add links easily by writing the word inside square brackets. Makes life 10000000x easier, trust me. For more information on how to do that, check out Help:Links.