To upload art you have to put:
-Upload
-artwork
-You only upload the file in Upload Source File
-Then in what are the categories and those things you don't need to put anything
-You must choose the rating based on the content of the art
-In the title you put the name that you want the commission
-A description where I recommend you put the minimum who made the commission, with :icon (username): a direct link to the artist will appear
-In keywords you can choose the tags just write them without more
-And then you just give Finalize

Hope this can help you! looking forward to seeing the commissions! >w<♥