Hey, welcome to steemit. Author rewards is what you get from writing a post. You will get 75% of all the rewards and rest goes to the curators. You will get 50% in steempower and 50% in steem dollars. Curator rewards come from upvoting and they're paid entirely in steempower.
You can get downvoted by other people if you are posting plagiarized content or behaving badly etc.

There is no notification system yet, unfortunately. There are some apps being developed for android like steemion

This should be pretty helpful and also try the search. https://steemit.com/steemit/@shenanigator/official-steemit-faq-rough-draft-your-edits-are-needed