Honestly speaking in simple words steem curator is the upvote you are doing on other post in which other person earn reward and you will get 25% funds whatever money or token he or she earn through his post. 25% is divided into all upvotes who has some value and rest of them are given to author.

Steem author is the writer of the blogs and the reward through which he earn amount of money by writing his post is called as steem author.