Can someone explain how the earning works on steemit ?

Hi all, Im new here.. And I read about how people even turn away from youtube to steemit and happy about it.
But I have some questions about it.

I think that you earn money by having your post upvoted ?

But, the person who upvoted this, does he have like an amount to spend for upvotes? Is he uploading his balance to upvote and donate upvotes to the community? Or is any users upvote worht a small amount of cash? if so, how did he received this cash? Do we have unlimited balance to upvote and donate to others by upvoting.

As you can see I still have many questions and I would like to better understand the whole system, where the money comes from, how it is earned, how it is donated or given away by upvotes and so on..

Can anyone help me with that ?