Learn about Simple Wikipedia by reading this article.
Any article on Wikipedia can be converted into plain English by changing the word en to simple in the URL. This results in a simple wikipedia article that is much easier to understand. Instead of manually changing the URL, you may want to use this bookmarklet on your browser:
Get bookmarklet: Simple Wiki
Whenever you are on a English Wikipedia page, click on Simple Wiki bookmarklet to get redirected to the simple version of the article.
The code does nothing more than changing en to simple in the URL.