1) There will be a post on Saturday, Jan 16 (tomorrow! yay!!) where you will be able to post your prompts in the comments.
2) The bit about the "screening" refers to comments when you actually sign up to participate in the fest and claim a prompt (on Jan 24). The comments will be screened. Meaning no one but the Snarry-a-Thon Mods and you will see your comment. That way none of the audience of readers or other participants will know which fic you wrote. But the participants aren't screened. All you need is a love of Snarry and a desire to write, draw, or craft.
There will be a call for betas closer to deadline, so you might find someone you can work with regularly. But the fest has volunteers who will be happy to beta for you.