Ooooh, awesome - a scanner is even better. ^-^
You'd put your drawings on the scanner glass (face down), press the "Scan" button, and it should open up some kind of program on your computer. Use that to scan your drawings - most programs will let you do a preview scan first, use that to tell it exactly what parts of the paper to scan.
Once you are done, it should offer you to save the file to your computer - put it somewhere you can find it again, such as your desktop. If it asks you for the file type you want to save it as, select JPEG for starters.
After you saved your file, you can go to devArt's upload, click "Add File" and select the file you just scanned. ^-^