You post whatever you want and depending on how many people see it and what they think about it you may get upvotes. Depending on how much Steem Power the user that upvotes you had you will get higher or lower payouts. Also, when you upvote someone else's content you will also gain a percentage back for yourself for curating.

I recommend researching topics you enjoy and sharing something with the Steemit.com users that you will both enjoy. Do not plagiarize, there are bots that will figure it out and then you WILL be forgotten about and no one will upvote you. Also if you use photos from out on the internet be sure to source them and if you are quoting, also don't forget to source.

Cheers and welcome.