How to add resource folder in java with standard tools in cmd or powershell

I'm new to Java and I'd like to know how do I add a resources folder to my Java project. I know how to do it in IDE, but for better understanding, I'd like to know how to do that in cmd or powershell with standard Java tools.

Thank you!

I'm using the following Java method:

private Image getImage ( String name ) 
{
    String filename = "/img" + name.toLowerCase() + ".png";
    ImageIcon icon = new ImageIcon
        (getClass().getResource(filename));
    return icon.getImage();
}

My project structure