It sounds like you may be using your public instead of of private key?

To access your private posting key, log into your Steemit account. Select "Wallet" then "Permissions." What is first shown are all your public keys, that allow you to encrypt communication to the blockchain. Your private keys allow only those with access to decrypt (i.e. control) the transmitted communication. To get your private key, click on the toggle button on the right.

Also, one of our founding members, Hive account@snakiest, put together a document that explains Streemian to a new user. But this also assumes you have created your account.

https://steemit.com/deepthink/@snakiest/deepthink-manual-how-to-join-our-curation

It I also assumes Streemian is working!