As far as i know application for the winter semester ended July 15th. Application for the summer semester 2013 usually begins in June. I dont know when you will graduate "high school" assuming its a Gymnasium you may need certain degrees depending on what you want to study afterwards. There are plenty of topics you can study without having super good grades though.
You said you want to study international relations. I did a quick research and found a few colleges/universities offering that topic.
I dont know which Frankfurt you are referring to (Frankfurt am Main or Frankfurt an der Oder) i assume you mean Frankfurt am Main.
The Goethe-Universität in Frankfurt am Main offers International Relations/Internationale Beziehungen
The "Freie Universität" in Berlin offers it aswell and im pretty sure they also offer video/editing etc.
You could also check out the universities in Baden-Württemberg. I read somewhere that they work pretty close together with american colleges and switching should be easy. Plus you are closer to the alps so skiing in the semester-holidays or on the winter-weekends would be possible.
You should be able to apply at an university online. Good universities offer their sites in english or other languages and you should be able to find the form for "foreign students" You fill that out and send it in online. You usually have to print something out and they tell you afterwards whether you can study there or not. Then they give you a date and you have to go there and confirm that you really want to study there. They hand you out your student-ID and usually tell you where your first classes are and what people you can come to if you have problems.
Sorry i did not double check what i wrote. Im German myself so please ignore grammar or other mistakes.
Shot me a PM if you want to know something else.
