If you want your virtual machine to start when host starts, there are two ways to do this. First one uses command line and pretty straightforward. Second one uses virt-manager (a GUI to manage kvm guests)
virsh autostart <domain>
Replace domain with your virtual machine name (case sensitive). For instance, if you have a VM named “websrv”
virsh autstart websrv
will mark websrv to autostart on host reboot/boot.
Open virt-manager and select your virtual machine from list.
Then display properties of virtual machine (i button next to computer monitor icon).
Select “boot” item from properties in the list (image 1):
Image 1: Virtual machine properties
From boot settings enable check box that says: “Start virtual machine on host boot up”