Mapsforge library how to create a map with the necessary objects?

Question

Cartography

Hello.
I want to try mapsforge to display the map. Only the road network and water bodies (large) need to be displayed. How can this be implemented?
1. Create a map with the necessary objects yourself? Then what is the best way to do this? Are there ready-made services/programs, or is it easier to write a Python script yourself to get data from the Openstreetmap API?
2. Set up the output of the necessary data in mapsforge? Is it technically possible at all? I did not find a clear description on the offsite.
I will be glad for any hints.