When a post gets paid out 25% of the value is split up amongst the people who have upvoted the post. The largest shares of the curation go to the people with the biggest votes. It also helps to have upvoted the post early after it was posted.

For a new steemian with low Steem Power you could be the first to upvote a post that ends up making 200sbd and your curation rewards would only be something like .002 . Don't worry too much about curation rewards until you have over 1000 Steem Power built up. Focusing on making good comments on other blogs with help you earn rewards the fastest.