It's about anything you want it to be.

The idea is to write posts, about the things you care about, or think that otther users will find interesting. If they do, they will vote for you. Of course you can also read the things others have written and vote for them.

If you like specific authors, you can follow them so that you automatically get all of their posts in your feed.

I personally would advice writing about 1 or a couple of things which you have a passion or a deeper knowledge of. This generates a public which is interested in those topics. But ofcourse, many people have been succesful writers here, writing about anything that comes into their head.

Best advice: write what you like, and because you like it. Not because you are chasing popularity.