WordPress.org

Read as startup : http://dpotter.net/Technical/index.php/2008/03/04/nextgen-gallery-review-introduction/

When writing a page/post, you can use the follow tags:

For a slideshow : [slideshow id=x w=width h=height]

Example : http://nextgen-gallery.com/slideshow/

For a album : [album id=x template=extend] or [album id=x template=compact]

Example : http://nextgen-gallery.com/album/

For a gallery : [nggallery id=x]

Example : http://nextgen-gallery.com/gallery-page/

For a single picture : [singlepic id=x w=width h=height mode=web20|watermark float=left|right]

Example : http://nextgen-gallery.com/singlepic/

For a image browser : [imagebrowser id=x]

Example : http://nextgen-gallery.com/image-browser/

To show image sorted by tags : [nggtags gallery=mytag,wordpress,... ]

Example : http://nextgen-gallery.com/gallery-tags/

To show tag albums : [nggtags album=mytag,wordpress,... ]

Example : http://nextgen-gallery.com/albumtags/

A further FAQ you can found here : http://alexrabe.de/wordpress-plugins/nextgen-gallery/faq/

And at least request your question here : http://alexrabe.de/forums/