Have you tried reading some tutorials? [https://nim-lang.org/learn.html](https://nim-lang.org/learn.html)
There are also videos at youtube. Generally in Nim we do not but all objects in its own source file as it is common in Java. So generally You just create one single text file for your code, and you import modules like strutils, sequitils, tables or whatever you need. Many stuff is already available without import from system module. For libraries not directly available in Nim we have external packages and the nimble or nimph package manager. Of course when your own code grows it may make sense to divide it in multiple modules. For a chess game you may have your module engine for the chess algorithm, and your module board for the display. Maybe one more for saving games to disk. The official tutorial has section about modules: [https://nim-lang.org/docs/tut1.html#modules](https://nim-lang.org/docs/tut1.html#modules) I have also written something about modules: [http://ssalewski.de/nimprogramming.html#_modules](http://ssalewski.de/nimprogramming.html#_modules) The other tutorials may contain more details.
