hi Pierrot,
this command is supposed to be done on the domain controller hosting CA certificate services as per the guide, and it's used to extract the previously configured windows noob issuing CA certificate to a file (any name you want eg: somecert.cer but makes sense to actually name it what is is, in this case windowsnoobIssuingCA.cer), for later import.
the -ca.cert merely instructs certutil to retrieve the CA's certificate, in this case, retrieve the windowsnoob Issuing CA's certificate,
does that make it clearer ?
if you then type certutil (with no options) on the domain controller, it should return the info you've previously set for the Config switch, such as in mine, below:
cheers
niall