Use SharePoint 2010 Groups with Team Sites
SharePoint 2010 uses groups to manage the process of granting someone access to the content in a team site. Each SharePoint group maps to a set of permissions that define the tasks that a user can perform. Most of your users fall into one of SharePoint’s three default groups:
Site Members: Confers the Contribute permission level for users, which allows them to add, edit, and modify list items and browse sites. Most end users fall into this category for a team site.
Site Owners: Grants full control. A site owner may or may not use the site on a regular basis, but the site owner can delegate administrative and design tasks to others. Also, a site owner may or may not be a technical person.
Site Visitors: Have read-only access to the site and can create alerts. Users who need Read access to a site but don’t need to contribute content are visitors.
Access to your site and its content is managed through group membership. Adding and removing users from SharePoint groups is the most efficient way of granting and revoking permissions.
A top-level site has a single set of Site Members, Site Owners, and Site Visitors. The actual names of the groups are determined by the name of the site. For example, if your site is named Projects, SharePoint calls your groups Projects Members, Projects Owners, and Projects Visitors.
These three groups are created and named when the top-level site is created. All the lists, libraries, and subsites that are created below the top-level site use these groups and have the same set of people inside the groups. By default, all the content and subsites in your top-level site have the same permissions, dubbed permissions inheritance.