There are different types of security implementation methods in qlikview. It depends on your requirement.
The Major Methods widely used are, 1. NTFS
In NTFS or Windows Security System, all the privileges and rights for users are assigned by Windows USer Management System.
While DMS is the Native QlikView Security Implementation Method where you can give the customized set of rights to the users. DMS = Document Management System.
This method is used to manage the document access rights to the users.
The above two methods can be implemented in the Server Management Console.
There is another method called section access. This can be implemented at the document level during the development phase of the application.
For more information, have a look at the server reference manual.