When was steemit launched?

when was steemit launched?

I dont know much about it except few things like it is the first blockchain social networking site. steemit gives money in the form of steem power, steem token and steem dollar. but I dont know how to earn money even I dont know how to write a blog.

I have few questions in my mind like what is curator? and how steemit gives money to a particular blog or post. I mean what is the criteria to give the money. its so confusing.

can anybody help me and tell me when it was launched?