So how do we put VM's on a server out on the internet?

My title probably sucks but i really dont know how to put it properly. Maybe i can explain better like this.

So in scenarios where we got a server(spec dont matter) and on that server we got 4 VM's running whatever they running. How do companies(data centres and hosting companies) actually put these out? I know that, if there is only 1 ethernet port that u can setup VM's to share it but this makes no sense if these VM's are for someone else.
My logical thinking:

1. If they got 4 VM's then they get a NIC with 4 ports, 1 port for every machine.
   

Or do they somehow route the traffic between VM's in a localized network(network between hypervisor and vm's)?