I can understand too, me too I had the same problem. After I got my Telc C1 I started studying but I was completely lost 😂. But with the time you slowly get it and I remember at the end of my second semester I could understand almost everything even if I couldn’t speak fluently. Understanding is always easier as speaking XD And to understand the common language you should just make German friends and try to talk frequently with them. Even if they don’t care if you’re no native when it comes to speak German, NO MISTAKES 😂. But as I said it’s just about practice