Just as for the main/primary domain on your account, you need to configure any additional domains to point to your server. You can do this by either setting NAMESERVERS
at your domain registrar to point to your hosts DNS (or whoever's DNS servers you are using). Or, set an A
record in the current master DNS records for the additional domain (which maybe at your domain registrar) to point to your application server. By changing the domain's NAMESERVERS
to your hosts DNS then your host will manage the appropriate A
records for you (when you configure "Alias" or "Addon" domains in cPanel - next step).
You must then configure your web host to accept requests to this additional domain. In cPanel you do this by creating an "Addon" domain or a Domain "Alias" (formerly called a "Parked" domain). If configuring WordPress multisite then you probably want to create a Domain "Alias", which simply maps the additional domain to the root of your account - essentially mirroring the main domain (WordPress then controls which site to display for the requested domain). An "Addon" domain generally points to a subdirectory (or rather, a subdomain) off your main account - which is more appropriate for creating entirely separate sites.