[Plugin: NextGEN Gallery] Captions

I am trying to add captions to my thumbnails. I added this shortcode
[ nggallery id=X template=caption ]
to my page right after the gallery shortcode on my page. I then wrote something in the image description under manage gallery. Is this how it works? I couldn’t find anywhere that actually read “caption” to write.

https://www.ads-software.com/extend/plugins/nextgen-gallery/