virt-manager is a gtk interface that connects to libvirt.

If you have networking problems, make sure you have the tun module
loaded.

To run virt-manager as a normal user, you need to configure libvirt
to have the correct permissions. Uncomment the unix_sock_group and
unix_sock_rw_perms in /etc/libvirt/libvirtd.conf and add the user to the
group libvirt uses.