Need an explanation of how Steem rewards work

I've watched numerous videos and paged through the whitepaper, and still don't really understand how author rewards and curation rewards work. 

I understand the basic premise that for author rewards, I am rewarded based on the number of people who upvote my post and also the reputation of the upvotes (measured by Steem Power, I think?).

What about for **curation rewards**? From what I understand, if you upvote content that later gets popular and has a lot of rewards, you get a certain cut of that? But if you upvote that same content after it's already popular, you don't get as much of the reward? Is there a formula to determine this? Is the amount of curation rewards you can earn somehow tied the amount of Steem power you have?

If there are any good explanations already out there about this, please share the link.

Thanks in advance.