Mining is no longer possible on the Steem blockchain.
When the Steem blockchain was originally set up, one option to earn Steem was by mining, or "Proof of Work". This was used as a method for the initial distribution of the currency.
However once the Steem distribution reward system was set up ("Proof of Stake / Brain") there was no longer a need for mining to distribute the currency.
As such Steem mining was halted with the Steem 0.17 Change Proposal at the start of 2017.
You can read more about it here:
https://steemit.com/steem/@steemitblog/steem-0-17-change-proposal-introduction