Add Media First
After adding media to a content editor (WYSIWYG), you can add a caption and change the alignment of the media item.
1. After you've added an image, audio, document, or video to Body or Content fields using the Media button  in the WYSIWYG content editor, you can set the alignment and add a caption.
2. Click Edit media  at the top left of the media item.
3. On the Edit media screen, choose an option to Align  the media item.
4. Select the Caption checkbox  to add a caption.
5. Display Options: You can change the size of media items. The Display options include: Default, 1/2 column width, 1/3 column width, and Full column width.
6. Click the Save  button.
7. Enter Caption  in the area provided.