I have recently recieved many questions of posting fanarts here on TheOtaku, so here is the basics of doing such! This can be applied to submitting other works like wallpapers and ecards as well

STEP 1 : Finding the Submission Page
(presuming you already have your work ready to go and you just need to put it up) You can either go to any Fan Art page (or the page for what kind of work you would like to submit) like clicking on the Fan Art tab or your fan arts or the fan art section of your fav anime etc. then select the link that says "Submit" OR you can go to your backroom, and highlight the "Quick Submit" link on top of the page and click on "Fan Art" or whichever fandom you wish to share.
NOTE ~ If you are submitting a work for a challenge then go to the Challenge you are submitting it for and submit it from there!

STEP 2 : Filling out the Details
{order and fields slightly vary for other works}
TITLE ~ Required ~ It can be simple like the name of the character, or you can make it enticing so subscribers see the title and want to see it ^^
CATEGORY ~ Required ~ Is it from an anime, which one? Crossover? Original? Is it a book/movie/music etc. Choose where it is from, if you cannot find where it is from, then select "Other" Categories are seperated in alphebetical order in Anime/Manga, Video Games, TV, Movies, Books/Comics, Music, Internet, and Personal
"Is this a Fan Character" checkbox ~ Kinda Required ~ Check it if there is an OC (someone you made up for an already existing series) in it or leave it be if all the characters are cannon
TAGS ~ Optional, but very useful ~ Good tags are the characters' names, if it's a crossover then the series they're from, theme or action in the art
CAPTION ~ Optional ~ Describe what is in the work and/or your reflections on the piece or any insights you would like to share with your viewers
MEMBER DEDICATION ~ Optional ~ If you would like to dedicate this to anyone on TheOtaku, make sure their name is spelled correctly or you'll have to do it over again if you put in a user that does not exist. Just leave blank if there is no dedication
UPLOAD WORK ~ Required ~ Hit the browse button and locate the fanwork from your computer
SUBMISSION OPTIONS ~ Kinda Required ~ Default it submits is for publication which means you'll be able to see it on your profile. If it's a sketch or something you are still working on, you may change it to "store as a draft/sketch"

NOTE ~ Other than FanArts, for Fan Comics, you will create a series page first or choose a stand alone. In a series, you chose where the new page is going in Insert Page After. Wallpapers have different sizes that you can submit for one page, the widescreen dimensions are optional, but you must at least have one 4:3 ratio of the Standard size to submit (must be at least 1024x768). E-cards have the same format as the Fan Arts and have a strict size requirement of 350x350. Quizzes are in their own ballpark, so I made a tutorial to help through that.

Step 3 : Submit!
When you are all ready, hit the "Share Your Masterpiece" button. You should get a green Success box to show it went through. If it's red then it did not go through and should point out why it didn't (ie size requirements or not filling out a reqired part of the form)
NOTE ~ New members' submissions go through moderators to make sure you're not posting plagerized or inappropriate stuffs to the sight, so at first it will take about 24 hours to show up. After you have proven yourself to follow the rules for posting, your works will show up imediately after submitting

Hope that helps ^_^ HAPPY FANDOM!