Copy it from your wallet on Steemit. The keys you see on SteemWorld are the public ones. They are public because they are only being used for transaction signing checks (to see if it was your account that signed a transaction)
Your private keys are secret (nobody knows them and that is important) and they can be used for posting, voting (posting key) / transfers, market orders (active key), etc. The most important keys are the owner key and your Steemit password because with them one can change all your keys and take over your account.
As I said, copy the private posting key from your Steemit Wallet and it should work ;)
Hooray!!! You got through my thick head using bold to show me private posting key...that's the part I was screwing up!! Thank you, thank you! There are so many people I know that are wondering..I'm heading over to Discord to fill them in! Cheers :) And thanks again for such a cool creation!!