What is Libraries and Metadata?SharePoint Site Security.

A library is a feature in SharePoint that stores files (documents). Think of a library as a folder on your file system. For example, a library can be created to store resumes in the human resources team site. A library is usually created for a specific type of file. Libraries can contain metadata to describe the particular file in more detail and to make it easier to find.

Metadata are fields or columns you can add to a library that are attached to every file stored in it. For example, you may want to add a city metadata field to the resumes library. Everytime a new resume is uploaded to the library a city can be associated with the file. This would make it easier to search for resumes from a particular city.

Users and groups (domain or SharePoint) can be assigned permissions to a site.

The "Site Permissions" link is where you go to view and manage permissions for the site. If you simply want to add a user to a group that you know has access to the site you can click on the group link in the "Groups" section in the left-hand navigation. If you don't see the group just click the "Groups" link in the left-hand navigation and a list of groups will appear to the right.