All books that are normally free are automatically included in the sale (which means yes, my own "
We Don't Plummet Out of the Sky Anymore" is among the free short stories in the sale)... so if you are an author with a free work on the site, you don't need to do anything else to be in the promotion.
If you are normally charging money, then you will need to
opt in for whichever works you want included, and specify the promotion level you want applied to each.
- M.