Step 1: After a photo, video, PDF, etc, is added to your story, a field titled "Caption" will appear to its right. Select that field and type in your caption. There is a 150-character limit for each caption.
Step 2: If you would like to leave your story unpublished as a draft, leave the "Status" field as "Draft."
If you would like to publish the story, select the "Status" tab and choose the "Published" option.
Step 3: Click "Save Story" in the bottom right corner of the page.
Your story's photos, videos, etc. now have captions!
