For all questions you may have the Humboldt-Universität has set up an incoming students guide. You are able to access it here:
On the page of the International Club there is plenty of information given for students interested in an Erasmus-Exchange. They offer a language tandem/partner programme, a service for questions regarding Visa-issues, a Cultural Calender, mentoring possibilities and much more.
Just take a look at the University's main building, Room 3120, 2nd Floor (above Audimax) or at their homepage: