Before you start applying for places you need to investigate what funding is available to you for study in Germany. Check with the Department of Education (or equivalent) in your home country to find out if any funding opportunities exist. Once you know what your funding options are then look for German universities who are doing the kind of research you're interested in and apply to them. Remember that due to the very large quantity of speculative applications that academics receive from international students they may not even reply unless you mention that you have arranged funding.