Just adjust the values in the config area denoted at the top of the jnc.py file and execute the script.
By default, it will only download already purchased books from your library. It will also ask you if you want to follow series it does not know about yet and print avaliable volumes you don’t own of series you follow.
The script optionally supports auto order of books and auto purchase of premium credits.
For details about this, refer to the output of python3 jnc.py --help
It only work if you have an account directly with J-Novel.club. If you log in using Google/Facebook, this script will not work.
Since you need to put your E-Mail and Password into the script file, you are essentially storing your JNC credentials in plain text on disk. This means any program running as root or with your user will be, in principle, able to access those credentials. Whether or not you are comfortable with this is up to you.