Hey guys I have the following set up at the moment:
my two domains are both registered with a registrar.
I bought up an set up a vps yesterday with virtualmin and pointed my a names to the new ip and it propagated fine.
The second domain has always redirected to primary, and is still using 3-4gb of banwidth a day with old host.
If I point it’s a name to the new ip as well would I need to create a sub server for it or can i get away with just redirecting it under the system settings / redirects?
You can either make a redirect, or create an alias (not a subserver, in that case it would have a separate web file folder), that’s mostly a matter of taste. 
Thanks that helps a bunch!
Just wanted to confirm:
I went into my primary server. then create virtual server. I used the second name domain there and now I have an alias (it says alias of primary domain if I go to edit virtual server).
Am I done here and it will auto redirect to my primary domain or is there more I need to do?
That should be all, yes. It depends on what web software you use, and whether that software is prepared to serve its contents under two different URLs.
When you create an alias server, it’s not a redirection. Redirection would mean the user requests URL 2, Apache says “please fetch URL 1 instead”, and the browser does that automatically. That’s also reflected in the address bar.
In your case, Virtualmin configured Apache to serve the same site under two URLs. There’s no redirection and no address bar change.
If that does not work for you, create your URL 2 as a full server instead and configure a redirection to URL 1 under “Server Configuration -> Website Redirects”.