Core to the Steem blockchain logic is the action of posting. Posts are created by authors and then submitted to the Steem blockchain via one of the many front-end application available on the network. From there, the content is available for developers to display on their application as well as for curators to upvote or downvote the content.
The Steem blockchain will always contain the full edit history of posts and comments. The size of a post is limited to about 64,000 characters including formatting.