before looking at virtualisation, try asking yourself, for example a service that you want to set up. It will consist of the application itself, very likely a database server, maybe other stuff for caching and maybe storing files?
So the question is, do you want to set all these up in a single server? or do you want to split them up into multiple servers?
Then, let's say, you have 2 web applications that you want to host at home. Do you want to install both on the same server? or do you want to split them up so they'll be easier to manage, and will not end up effecting each other if you happen to update dependencies for one of them.
With this in mind, if you decide to split up the servers, with virtualisation, it allows you to run everything in a single physical machine.
As for how you are going to access the installed OS, that depends on your network setup. on if your VMs are host only, or are they given individual IP addresses on your network
Why multiple VMs on a server?