Question

need to properly reference a web site http://www.nga.org/cms/home/management-resources/governors-powers-and-authority.html
and cite it

Answer 1

Cite it as you would any other organization for the format you are writing in. For APA the first citation would be (National Governors Association [NGA], 2011). Subsequent citations would simply be (NGA, 2011).

Answer 2

Reference page entry would follow the same rules as an organizational reference entry:

Organization. (Date). Title of article. Retrieved from http://whatever.com/article

That also is APA. Consult the guide of whatever format you are writing in.