What is a Studienkolleg?
If you aren’t quite where you need to be to be admitted directly to university, you can participate in a Studienkolleg for a year beforehand to prepare a qualification exam for the university. This is a prep course in the area of the subject you want to major in, consisting of 28-32 hours per week. You will be with other foreign students who also want to get into the German university. Generally, you have one year (2 semesters) of Studienkolleg before you take the exam, but you can also take it after 1 semester if you do well.
How do I enroll?
To enroll in a Studienkolleg, you need to meet the following criteria:
You are going to need to pass your DaF or DSH test.
US high school diploma with a GPA of 3.0 or better (see above)
Some helpful links:
Here is a good website showing what you need to know to enroll in a Studienkolleg: http://www.studienkollegs.de/miniwebs/studienkolleg/en/14309/index.html
Here is a good website showing an overview of admission criteria: http://www.studienkollegs.de/en/14424/index.html
In order to see what Studienkolleg you will need to enroll in (you will have to enroll in one similar to the subject you want to major in), check here: http://www.studienkollegs.de/en/14418/index.html