Register an account at ND.
Log into your registrar and see if you can export an Excel file of all your domains, if so, copy and paste the contents of the file in the
"ADD DOMAINS" window at ND. (if you cannot export it, or don't have many domains, do it manually)
ND has a Help and Setup section where you can retrieve the NS-NameServer settings and the forward URL if you chose to use it. Copy the Nameservers and enter them into the NS field of each domain ON YOUR REGISTRAR SIDE. As this is the only way to direct your domains to show the ND content.
Inside ND - Access each domain in its settings and tweak it with appearance, content, keywords, etc. you can preview each domain with the magnifying glass.
Once satisfied with the looks and the keywords that you selected, save each domain.
You also have the option to specify folder, which comes in handy when you have 30 car related domains, then you mass specify the settings for the entire folder and just adjust the keywords for each domain.
That's pretty much the skinny of it all.
If you need any more help, there are tons of Parking specialists on NP.
Best of luck!