What is SSL Heartbleed Bug in simple English?
Basically it is a program bug/vulnerability in the SSL/TLS encryption that is widely use by most of the Internet applications such as website, VPN, email, etc. This allow the attacker to read/steal the your communication information. For more detail, you can check out http://heartbleed.com/ and http://www.kb.cert.org/vuls/id/720951
How to test Heartbleed Bug
Below are some of the useful links that allow you to check whether your HTTPS website is vulnerable to Heartbleed bug
Qualys SSL Labs: https://www.ssllabs.com/ssltest/
Heartbleed test: http://filippo.io/Heartbleed/
Critical Watch Heartbleed Tester: http://heartbleed.criticalwatch.com/
LastPass Heartbleed bug test: https://lastpass.com/heartbleed/
Heartbleed checker: http://possible.lv/tools/hb/