A profile contains user permissions and access settings that control what users can do within Salesforce, the partner portal, and the Customer Portal.
Depending on which profile user interface is enabled in your organization, you can:
§ Which standard and custom apps users can view
§ Which tabs users can view
§ Which record types are available to users
§ Which page layouts users see
§ Object permissions that allow users to create, read, edit, and delete records
§ Which fields within objects users can view and edit
§ Permissions that allow users to manage the system and apps within it
§ Which Apex classes and Visualforce pages users can access
§ Which desktop clients users can access
§ The hours during which and IP addresses from which users can log in
§ Which service providers users can access (if Salesforce is enabled as an identity provider)
Chatter customers (users with the Chatter External User profile) can only see groups they belong to and people in those groups; they can't see any Salesforce information. If your organization uses a custom domain or IP restrictions, it's recommended that users with the Chatter External User log in using single sign-on.
Every organization has standard profiles. In Contact Manager, Group, and Professional Edition organizations, you can assign standard profiles to your users, but you can't view or edit the standard profiles or create custom profiles. In Enterprise, Unlimited, and Developer Edition organizations, you can use standard profiles, or create, edit, and delete custom profiles. For standard profiles, only certain settings can be changed.