You answered well, but I think I’m not getting you fully yet. I just created a new hosted domain in the control panel, and I assume I have to assign those three NS in my new domain properties.
On the other hand, I’ll explain myself better. I have a domain and a hosting service already in Dreamhost: www.scopealley.com. A friend just bought www.throughthelenses.com and I set up: bucky.scopealley.com for him, with a new FTP user and stuff. I wanted that www.throughthelenses.com to use bucky.scopealley.com sub-domain hosting, so I went to this one DNS’s in control panel and I saw this:
bucky A 18.104.22.168
ftp.bucky A 22.214.171.124
www.bucky A 126.96.36.199