My first Steemit story

Well hello there my fellow writers/readers/fans :).
I would very mych appreciate if any of you could teach me about steemit and how it works.

1. What am i allowed to write about?
2. How long should the article be?
3. Can i post only pictures? Like a photoblog?
4. Can i realy make money with steemit just beeing myself?

Thank you fellow Steem-ers!