When users can access Site.com in the Force.com app menu in the Salesforce header
After you allocate a feature license using user details page provide the below permission then users can access Site.com in the Force.com app menu in the Salesforce header.
- A Site.com Publisher User feature license, select the Site.com Publisher User checkbox.
- A Site.com Contributor User feature license, select the Site.com Contributor User checkbox.
Make sure “View Setup and Configuration” Permission is enabled.
There are three roles at the site level:-
1) Site administrator – can create and manage all site content. They can create sites, templates, style sheets, and pages, and also set up domains, publish sites, and assign user roles
2) Designer – Same Control like Site Administrator to modify content, but they can’t manage domains or publish sites.
3) Contributor – most restricted access to content and can typically just edit page text and images
Source:
https://help.salesforce.com/HTViewHelpDoc?id=siteforce_admin_setup.htm&language=en_US
Site.com Workbook: http://www.salesforce.com/us/developer/docs/workbook_siteforce/