Or i can just to it here. I'm sure you know the basics, going up to 'Submit Art' and clicking that. Everything there is pretty self explanatory. For the catagory of the piece i've been using Fanart > Digital Art> Other. SUpload the image, add a description, add a few tags (words people type in the search bar that could bring up your piece) and hit the Button for 'Not Mature Content' and voila!