If you want something really simple, you can use WordPress gallery shortcodes. Without adding any plugin at all.
Simply create a post or page and upload pictures to it (“Add media”). Don’t click the “Insert into Post” button, though, just upload the photos, close the media box and write this in the body of the page/post:
[gallery]
You can also specify some options, for example:
[gallery size=medium columns=4]
Here are a list of options you can use:
http://codex.wordpress.org/Gallery_Shortcode
