Gallery, adding images

I am a developer who is new to wordpress,
I know I am overlooking something simple..
here is my issue…

I am having a problem discerning how to add images to the Gallery tab in my media library.

My goal is to make a image gallery with wordpress to showcase
the work of a tattoo artist, I can get the gallery to work,
but only one image at random seems to go into the gallery
section.

How do I add images into the gallery tab?

ciao
-omdyn