How does time work in the Netflix series Dark? CAUTION POTENTIAL SPOILER?

I have just arrived at the end of season one and have not (yet) understood the concept of time and time travel. If that should not be the case at this point, please say so. So: You can travel from 2019 to 1986 and 1953. But can you change the future now or not? I mean Ulrich will have (at least minimally) influenced the future with his attack on Helge. According to the authors, it should be like Harry Potter, but that didn't really help me either

The next two seasons will deal with the question of whether or not you can change the time loop, so just keep looking.