Site Administrators have the ability to grant and revoke permissions. If you are a site admin, there are two typical ways to grant access:
* Add the person's NSID into a security group on the Active Directory (recommended).
* Add the person's NSID to a SharePoint group.
Using either Active Directory or SharePoint security groups are the best way to add and remove people's access to SharePoint. It is possible to grant someone access to a site (or a portion of a site) without using a security group, but we strongly suggest you use security groups to make management easier (and less susceptible to mistakes).