This is the post explaining how to use AO3 to sign up. Click images to enlarge. (Text description is provided below--please contact us if you have trouble viewing the images/signing up.)
Note: Your writer/artist will see all the details you put down in the request (e.g. pairings, categories, etc) though we can only guarantee matching on characters.
Enter 1-4 characters in the "Characters" field. Some of the characters' names already exist in the Archive, so they'll come up on autofill. If they don't, that's okay--just type in their name as best as you can. If the name comes up in another fandom, you might want to disambiguate by adding extra things (eg instead of simply "Amarante", use "Amarante of Namarre"), but we're handmatching and we know the fandom, so it's not a big deal.
Enter up to two pairings in the "relationship" field. This can be romantic/sexual relationships, or friendship. Use "/" to mean romantic/sexual, and use "&" for friendship. You do not need to specify relationships.
Pick up to six or "Any" category (F/F, F/M, Gen, M/M, Multi, Other). I've picked F/F here, because I want to request a pairing between Jehanne and Moirin.
Pick up to 4 ratings for your request, or use Any. If you use "Any", your writer/artist has your permission to choose any rating.
Put a link to your letter/prompt list in the "Prompt URL" box, if you're writing a letter. If not, you can fill out the details in the details section. You can fill in both!
Letters are usually written to give creators more of an idea of what sorts of things people like. Letters can be posted on any site, so long as it is publicly accessible for your author. Common places people post letters are LiveJournal, Dreamwidth, and tumblr.
Optional tags: you MUST specify if you want art or fic. Here, I just want art, so I've written "art".
At the end of the third request box, there is an option of requesting up to 3 more requests (up to 6 requests allowed). Click on it to open more requesting boxes.
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Offers!
Like the requests, enter the characters you are willing to create art for or write. Please offer only what you can do! Panicking after receiving assignments is a time-honoured tradition but please make sure you're offering something that you're able to do. You can offer Any. This means you may be paired with someone requesting any character in the entire Kushiel universe.
You can offer up to 15 relationships in one offer, and any combination of categories or "Any".
Also like the requests, you can pick a rating. Do not fill in the prompt URL or the description boxes--they're not necessary.
If you would like to put in an additional offer, click the button to the bottom right of the page "Add another offer?"
In the "Optional Tags", specify if you're willing to OFFER art or fic.