How can I add descriptions to Gallery Images?

Good day Lindsey,

All you need to do is click on the ‘Gallery' element and select ‘Edit Gallery’ option.
Here and now, you can change/add Alts, Titles, Descriptions  for every single image as well as Links to redirect your visitors to other pages.

To do so, simply select the image and you'll see the options available on your right.

Hope this helps.

-Ines.