The idea was described in a whitepaper released in March 2016 which was updated in August 2017.
The general concept is similar to other blogging websites or social news websites like Reddit, but the text content is saved in a blockchain. Using a blockchain enables rewarding comments and posts with secure tokens of value. Images can be uploaded and hosted on Steemit. Other multimedia content must be embedded from other web hosts. For formatting, there is a WYSIWYG editor. Users can also opt to use Markdown formatting with HTML elements.
User accounts can upvote posts and comments, and the authors who get upvoted can receive a monetary reward in a cryptocurrency token named STEEM and US dollar-pegged tokens called Steem Dollars. People are also rewarded for curating (discovering) popular content. Curating involves voting comments and post submissions. Vote strength and curation rewards are influenced by the amount of STEEM Power held by the voter.
Steemit has a reputation system, where new accounts start with a reputation of 25. An account's received votes can influence its reputation up and down, incentivizing online etiquette and interaction with the community.