Sorry, it's a slightly snarky comment. Basically, you can find people's public posting keys (in the permissions section, mine is STM67FF7M6sXcugrrEEyPWeH2HZCa5PNoxx4NR3URmYeGVAz4tDHz). You use it to encrypt your message. Then I use my private posting key to decrypt it.

For your reading pleasure:
https://en.wikipedia.org/wiki/Public-key_cryptography