How to embed and edit a google doc within a google site?

A group I am involved with is using a google site to collaborate and store documents. We would like to have the functionality of google docs directly within the google site. Specifically we want to be able to edit documents collaboratively in real time just like in google docs. For some reason I’m having a hard time figuring out how to do this; it seems like it should be easy. Maybe our group should just be using google docs, and not have a google site. . . ?