This Links Block allows an Administrator to setup links - see the Block top right. But the cool thing is that it can show different links to different users, based on information in their Profile fields! By default it support user fields Institution, City/Town, Department, and Country.
If you Login here as a Teacher (teacher1/teacher1) you will see the HR link because your Department on your Profile is set to HR. If you Login as a Student (student1/student1) you will see the links change