Adding multiple domains to account

I don’t think you are really asking about multisite WP — where one WP install shares the WP core files, plugins & themes.

You are simply asking how to add a second WP site to your hosting account, right?

Some of this will vary by the hosting company, so you might want to be sure to consult their support documents & support reps.

Generally, you would point the domain to your hosting company, and generally, add the domain in your hosting, which normally creates a subdirectory in your file manager. So for instance, maybe the additional domain you want to use is “seconddomain.com” and the main domain in your hosting account (the one with the WP site already installed) is “maindomain.com”. Once you point & add domain, you might get a new folder “seconddomain” in the root level of the account — in the same folder as the wp-admin folder for maindomain.com site.

You can then use either an automatic installer or manually install WP in that “seconddomain” subdirectory.

HOW you point & add that domain is what you should ask your hosting company. ??