You are asking a very general question, with a very specific reference to a particular package, yet without any runable code, or what “does not work” means in this context. This makes it hard to help you.
That said, I am guessing that you want to define a method for OpenStreetMapX.distance. Either import it, or qualify with the package name. Please read
https://docs.julialang.org/en/v1/manual/modules/
Also, you seem to be asking a lot of general Julia questions here (which is fine), but all somehow involving OpenStreetMapX. Even if your work focuses on this specific package, I would suggest that you consider reading the general Julia docs multiple times carefully, so that you gain a better understanding about the language. I think it would help you in the long run.
Finally, please consider reading