What exactly can the police do, according to law and what not?

Hello, I’ve been here lately, more and more in police controls. Sometimes you feel very much disturbed in your privacy or you’re being stopped without suspicion for half an hour. That’s why I’d like to know what the police can do. So suppose I’m coming right after entering D. from the Czech Republic into a drug control. I think the colleagues were either from the Bavarian police or customs. But they looked more like police officers. Not every car was waved out for drug control. Well, at least the first policeman only meant that I was only checking my data for a short time. Suddenly, however, my car was searched. I should even step back from my car when I was searching… But here on the net it says that you can stand next to it when the private things are being searched. 2. I really can’t use it anymore when every policeman at the border in my Wasc What’s that supposed to mean? I don’t think that most of what they do, at all. Why else does the policeman ask me to open my laptop bag? Can’t he do it himself? Probably he can’t at all. Nen else I should open the travel bag. I’ve already read on the net that the police can’t search at all without a suspicion. That she can only check the first aid kit. So you say “Darf ic What if I say no? May the customs or the police, 500m after the border (there is no house anymore), then search me without a court order, without any evidence of drug possession?