You are not required to post your story/art to AO3, but we encourage you to do so. It lets us have a central location for all of the Big Bang fanworks, and also, as you probably know, all stories are easily downloadable in e-reader friendly formats; this is particularly nice for your fellow fen with health issues or those who just plain love their e-readers.
The collection for the current year is Pros Big Bang 2019. (Previous years' collections are accessible here.)
Sineala wrote up a little guide for how to post to AO3 for the Big Bang; the same directions apply, except that you'll want to make sure you're in the 2019 collection this year.
If anyone who doesn't have an AO3 account and wants one, let us know.
If you have stories/art from previous years that you have not yet posted to the AO3, we have left the previous collections open for exactly this reason. Feel free to add your Big Bang story or art to the appropriate year's collection.
Happy posting! Let us know if you have any questions and we will attempt to confuse you further, ah, I mean help, of course! =0