WP Beginner needs help adding captions to images

Most basic of all. I’ve uploaded a few images and added them to a test photo gallery but I can’t figure out how to edit them to add captions to the images for use later. I couldn’t find a way to add or edit “Captions” in the Photo Gallery and for some reason, the images don’t seem to be part of the Media Library. I checked the online manual under images and couldn’t find and topic headings having to do with adding/editing captions.
Any assistance would be greatly appreciated!