If you want to apply for admission to one of the structured PhD programs (click here to see the list), you don't need to apply to the Beijing Office of Freie Universität Berlin.
You have to apply to the program you are interested in, instead. In order to do this, you have to go to the homepage of the program first and check out their admission policy towards foreign PhD students coming with their own scholarship, i.e. in your case a CSC scholarship. Then you should write to the contact person of the respective program.