I Googled a question (can't remember what it was), and this site showed up the search results. Someone on here asked the same question. I browsed around the site, liked the was it's set up, and everything else, so I joined.
An acquantance of mine posted a link to a question she wrote here, I answered and then just stuck around because there where more answers to give. Oddly enough I got addicted to giving insight to people here =)
Honestly, I don't remember. Maybe Google? I like it so much better than Yahoo! Answers and it's not as judgmental as the commenting "cliques" on many other websites. I made some great friends on here, so I'm very happy I found it too. :D
I typed in how to get over an ex then the site showed up!