VestaCP handles server block creating and setup when you add a new domain through the CP. You shouldn't have to physically modify the NGINX server blocks yourself and it's actually advised that you don't as VestaCP may overwrite changes that you made.
To add multiple domains, you'd simply login to VestaCP and create each new domain. VestaCP will do the setup for you, so all you'd need to do is upload your files to the directory that was created for the domain you just added.
You can check
/home for the corresponding directories. They are separated by username, starting with
admin. Each user you create through VestaCP will have their own home directory as well, so if you create
/home/myuser will be the home directory and domains will go under that directory: