Hey there. See that dark green bar at the top? There should be your user name...well there is a button called "submit" three arrows on the right. Click on that. Then you need to give your work a name, put it in a "category" of art, then you have to upload your piece of work. You can also set the size people want to see it. Further down the submit page, you will have to "check" boxes if yes or no it's "adult" work, and your agreements to deviantArt's policies.
Then you click on OK/SUbMIT(don't remember the button's name)and you should be done! : ) Hope it works out for ya.