Can we create a New Site and access it without a domain?

On my VPS I have one site linked to a domain and ERPNext is working like a charm.

I want to add a new site but I do not want to assign it a domain/sub-domain.

I have never done this and am afraid that if I try something the main EPRNext setup will stop working.

How can I add the site and access it using the primary domain that I have linked to the VPS?