All parameters contained in JS config file are detailed on Filemanager configuration file wiki page.

Just copy the content of "/scripts/filemanager.config.default.json" into "/scripts/filemanager.config.json" and load the filemanager into your web browser, it should work.

The server root directory is automatically detected by the application and the default files repository is located into "userfiles/".

By default, fileRoot is set to false. In that case serverRoot value is not interpreted by the filemanager and considered as always true.

        "serverRoot": true,
        "fileRoot": false,

If serverRoot is set to true, the application will search fileRoot folder under server root folder. You can specify manually fileRoot folder

        "serverRoot": true,
        "fileRoot": "myapp/media/",

Don't forget the ending slash to fileRoot value. Note that there is not starting slash since it is added automatically.

Set serverRoot to false and set fileRoot to the desired folder, for example "/home/johndoe/myfiles/". Be sure the server user has READ and WRITE permissions on that specific folder.

        "serverRoot": false,
        "fileRoot": "/home/johndoe/myfiles/",

Don't forget the ending slash to fileRoot value.

see How to allow users to have their own folder