Here you can digest how to use Wikipedia, in bite-sized morsels. The tips listed below were created for the Tip of the day project, or the Styletips project, but are listed here by title and organized by subject area for your convenience.
You know normal links—they look [[like this]]. But did you know that you can use normal links to pages on any other wiki? This is called InterWiki linking, and applies to all wikis, not just Wikipedia's sister projects. You can link to a page on MeatballWiki by typing [[MeatBall:PageName]], for example. See Interwiki map.
However, links to Wikipedias in other languages are done a little differently. You can link to these by typing, for example, [[:de:Hauptseite]] (replace "de" with language prefix). The colon at the beginning prevents the link from becoming an interlanguage link, which shows up in the left sidebar.
To hide the prefix from the link, use the pipe trick.
Bonus tip: the same basic syntax works in the search box. (Try typing in Meatball:)