Thank you very much for your answer. Well, without having read it yet, I have done pretty much as recommended. After sleeping on it for a night, I installed it again and watched an introductory video. In the meantime, I can create a new airplane, but I already manage to close the front flap. I'm getting familiar with it, but it will still take a lot of time.
However, I have a question in a new thread that I have not yet been able to solve.
Switching the MDF, for example, to get the hydraulic display shown in the introductory video.