Can be found on the Official FAQ.
“Yuletide can be an intimidating exchange for the new participant. The rules can be complicated...Beginner's Guide to Yuletide
“Sign-ups for Yuletide generally run for one week in mid-to late- October barring any unexpected...Yuletide Sign-Ups
“Every year the list of eligible rare fandoms from which participants can request/offer fics...Yuletide Nominations
“Each year there are requests that do not have writers, either because they were unable to be...Pinch Hitting
“Each participant is assigned one other participant and is required to write exactly one fic for...Yuletide Assignments