Question about voting on posts in STEEM

Hi,

I'm still struggling with some basic concepts.

It is my understanding that an upvote on a post is not a transfer of STEEM to that post from the voter to the author of the post, but merely causes the author to get STEEM.

I neither understand where that STEEM comes from (inflation?) nor what would stop an abuser to create sock accounts and upvote his own posts.

Does somebody have a link that explains this in more detail?

Thanks, John