KoolReport and each packages may contains js/css resources that needs to be accessed from browser. Those resources are normally go with packages and many times in inside the "vendor" folder which is prohibited to access. That's why those resources needed to be publish to a public place.

What does it mean by "automatic"? Meaning that you just need to use koolreport without care about the resources. If KoolReport find that resources is prohibited to access, it will try to export resources under a folder name "koolreport_assets".

When you use Laravel package. This package contains the guide for KoolReport to export resources. It tell KoolReport to make a folder "koolreport_assets" under "public" folder of Laravel so that those resources can be accessed. So if you use Laravel package of KoolReport, you do not need to manage the resources.

Those "number" folder is just a random named folder to contains resource of KoolReport's package. You can delete them all and it will be published again when KoolReport need resources.

Beside of "automatically" handle the resources, you can manually handle resource via "assets" in settings()

class MyReport extends KoolReport
{
    protected function settings()
    {
        return [
            "assets"=>[
                "path"=>"../../public/assets",
                "url"=>"/assets"
            ]
        ];
    }
}

The path to let KoolReport knows where to export resources and url to let KoolReport knows how to access them from browser.

Hope my answer helps.

For your questions:

1. The files populated in koolreport_assets folder comes from koolreport packges in vendor folder.
2. If you delete contents of koolreport_assets, it will re-populated.
3. There is mechanism inside KoolReport to detect if there is the lack of resources. If there is, it will populate.