Amazing =)
And it's not a stupid question at all!
I've got this from the web because I've feared you might not understand my way of explanation...
An author's note is created by a writer to guide a reader's response to his/her work; author's notes typically explain where the piece is in the writing process, what the writer thinks is working well, where the writer feels stuck or needs feedback, and what kind of response the writer hopes to receive
In this case, the author's note is there to let your readers know what the contest is about, who's running it and (if you want) to tell them how you got the idea, what inspired you etc. The author's note is mostly put in the beginning.
I hope that helped!
Merry Christmas to you.