To use just, first make a file named Justfile and put it at the top of your project.

project/
  dan.da.dan/
    src/
      module-info.java
      characters/
        MoMo.java
        JiJi.java
  Justfile

In this file put the following contents.

help:
    just --list

This makes it so that if you run just or just help it will list the "recipes" available for the project.