Answer:

Go to your workspace by clicking "my workspace" on the menu to the left. Choose the content you want to add from the "add content" menu. Then click "add new item". Follow the instructions on the form.

Offsite photos, audio and video are stuff hosted on other sites such as flickr.com, photobucket.com, youtube, myspace etc.

You can upload this offsite stuff by pasting the url from the page where the stuff is. In other words:

Go to say,  http://www.flickr.com
find a photo
copy the url -that's the address at the top of your browser when you are looking at the photo - by either selecting the url and clicking control + c on your pc or apple + c on the mac.

Then paste it into the space in the form you are presented with on this site.