Courtesy of Conde_Mohr.
If you have any questions or suggestions, private message him on Myanimelist.com or mention him in either of the discussion threads for the challenge.full pdf guide | excel sheet @ dropbox | excel sheet @ google | excel sheet @ 000webhost
This is a quick guide. For a more detailed guide, look at the pdf linked above.
In the file, there are 5 sheets: 2 for anime, 2 for manga, and 1 for the forum post. For either manga and anime, go to the Bonus Card sheet and write your bingo card number where indicated. Check if the automatic bingo card is the same as the card you received with the same number. If it's not, contact either the moderator of the challenge or me. Once you do that, choose your pattern and your additional rule (if you're making an extra challenge). The pinkish cell in the middle is the Free challenge, and you'll have to change that with the number of the extra challenge you're doing (it can't be repeated with a number in your card).
To update your anime/manga, go to the Challenge List sheet and, under the Anime/Manga column, write the item you have for that particular challenge. Challenges you don't have to do are grey, and challenges you have an anime for are blue. At its right, there's room for the status of the anime. It will change automatically to "Completed" or "Watching/Reading" according to the start/finish dates written in the following cells (it won't say anything if it's a planned item, as it defaults to it). At the right, there's room for start/finish date, the ID of the item, and any additional information that you want to write about it. Keep in mind that, for some challenges, it is compulsory to write something there.
For the Forum Post, you need to choose between the anime and manga posts, and fill the information in the poorly named "Other personalization" table. Once you do that, you can format your post with the options available, or even change the colours of the items depending on their status. Finally, you'll have to copy everything in the table on the right and paste it in your post as it is. If you did it properly, you'll have a valid post that updates with the excel file just doing that.