You can categorize your artwork by using the Albums feature.
To create an album, first navigate to your Portfolio Manager from your Avatar menu.
On the left side of the Portfolio Manager page, you have the option to create and manage albums. Click on "Create new album" and name it. If you have a Premium account, you will have the option to select its visibility. Click save once you are done.
Once you have created your Album, you can just click and drag a Project into the Album folder.