When you select the word, a small clover with four icons (one on each 'leaf') opens right above it. Each icon represents a website (you can select the four included ones yourself) where you can find information about the word, including Wikipedia, Google, YouTube, Vimeo, or Twitter, among others.
When you click the icon you're interested in, say, Google for example, a small Google window pops up alongside your window, showing the results without your having to leave the tab you're on at the moment. It's easy, quick, and convenient.
KwiClick is an extremely useful add-on for anyone who uses the Internet a lot, especially since nowadays, we're constantly searching for information about words or people we find unfamiliar.