I just installed a 7.5 server.
There is no webvirt manager and virtual machine.
How can I install it, or what is it for?
I would need a minimal windows virtual machine.
WebVirtMgr is no longer maintained upstream. An alternative is to use libvirt with virt-manager:
The WebVirtMgr project is no longer maintained and the corresponding module has been removed along with nethserver-libvirt package. See Virtual machines chapter for details on how to use virtualization
I would opt to install virt-manager on my desk/laptop. If I needed a seperate VM manager.
The easier (and IMO better) way is installing ProxMox and have NS as a VM on that.