Instead of me trying to explain all about it, I came across an article online from PC World that explains it much better than I can. Please read it. It's critical that you do. http://www.pcworld.com/article/2141602/the-heartbleed-bug-and-you-a-users-guide.html
Bottom line is, you need to change all of your passwords that you use to log on to any Websites or emails. But read this article first because if you change your password on a site that hasn't fixed the breech, then you've changed it for nothing.