This is a good time to cover the very important topic of site groups because it is important for Site Administrators to control who has access to their site collections. A Site Administrator can specify who can perform which actions in the site by adding users to SharePoint site groups. Larger organizations may already have Active Directory groups created that can be added to site groups, which can be a great timesaver.
Here's a list of the standard site groups:
ReaderHas read-only access to the site.
ContributorCan add content to existing document libraries and lists.
Web DesignerCan create lists and document libraries and customize pages in the website.
AdministratorHas full control of the website.
Custom Site GroupA Site Administrator can actually create a site group and call it whatever he or she wants (Super Reader, Limited Contributor, Power User, and so on).
A Site Administrator can grant special access to Web Parts within the site (such as a document library), so if you really need to be able to add documents to a document library, but are only a member of the Reader site group, the Site Administrator can give you enhanced rights to that library.
The assumption in Parts IIV is that you are a member of the Contributor site group. If you are a member of the Reader site group, you won't have access to all the tools discussed in the end-user lessons. So it's a good idea to ask your Site Administrator which group or groups you are a member of if you don't already know.