A blockchain is a database which lives in the Internet and is not owned or controlled by anyone. Any content that goes into this sort of database cannot be removed or altered by anyone except the author of the content. So it's 100% censorship resistant.

A blockchain can be used for many purposes. Steem uses blockchain to store blog contributions made by its users, to record interactions between those users (e.g. upvotes) and to facilitate the underlying payment system. So what you see right now on the screen is just the tip of the iceberg.