Okay, the other comment was actually pretty funny. But this one's a serious answer.
Transport Layer Security protocol is a way to share secrets. Basically, it's the lock on your airport luggage. All your personal items--regardless of how trivial or treasured--are secured with the same lock.
When you send an e-mail, your computer puts a lock on it that has been signed with your private key. It's sent to a recipient, who can unlock it with their own key. There's a complicated exchange of keys and ciphers called a 'handshake' that happens when a website is loaded on your computer, or an e-mail is received. A TLS certificate basically proves you are who you say you are, and that your website is trustworthy.
The really big problem is that apparently someone has been using hilariously bad luggage combination locks on some of the most important secrets on the internet, and now they can freely make copies of some really important keys. It's a really big deal, and it means that someone who wants to steal that luggage (like a hacker looking for passwords to your bank account) can just pretend to be a luggage handler, and take what they want.
