In case any other newbies have this problem with this particular theme again:
1. I picked out images that I liked, resized them to fit, and renamed them as dream0, dream1, etc.
2. The header images (labeled dream0, dream1, etc.) have to be uploaded into a folder named ‘images’. I didn’t have one and had to make one inside the /wp-content/themes/falling_dreams/ folder.
The code to rotate the images was already in the header.php file…I didn’t have to change anything in that file. The code calls for four images, so if you’re not using four you’ll have to go in and tweak the number so that you don’t end up rotating a blank, white space.