Once you have received the invitation to sit the entrance examination you will need to apply for a travel visa for Germany at your relevant German foreign representation (embassy, consulate).
Reason for travel:
Study, study preparation orvisiting the Studienkolleg
Depending on the country, a visa can take several weeks or months to be issued.
The visa is initially valid for 3 months and can be converted into a longer residence permit after passing the entrance examination.