The simple answer is that you can take photographs of paintings, sculptures, events and the like. Often the photos are already digital, and in most cases you can upload them directly and the site will automatically change them to the appropriate size. If you have photo prints instead of digital versions, you can digitize them using a scanner. It’s important to do the best job you can so the textures and colours show your work at its best, so you may wish to get a professional to do the job. Cosmic Idea can possibly do some of this for you (our rate is $50/hr.), and there are other folks who can help with this as well.
Text can be typed or pasted into the editing window on your profile pages. There is more information about this in the FAQ: How to Use the Site area.