Page groups is the generic Webstore name for any type of file uploaded to Webstore whether a web page or another type of file. See First Time Users start here for more information.
The Page Groups options menu varies a great deal according to the permissions of the user.
This for example is what an administrator sees when he/she clicks on a published web page group.
However, a writer would see this for a page they had uploaded
An anonymous browser just sees the option to 'View Page'.
Assigning Home pages is covered in Home Page(s).
Assigning Index pages is covered in Index Page(s).
All other possible page properties are covered in Change Page Properties.