kvm virtualization: how to add network settings to the startup image in the cloud to run a kvm image

I am trying to use cloudinit to activate virtual machines in a kvm hypervisor environment
I have downloaded the Ubuntu 18.04 image and created the following configuration file

package_upgrade: true
  - name: 
    groups: wheel
    lock_passwd: false
    shell: /bin/bash
    sudo: ('ALL=(ALL) NOPASSWD:ALL')

I can activate the VM and log in through the console.
I looked around but couldn't find any information on how to configure my network
I like (interfaces, IP addresses, …)
the cloudinit documents I looked at I couldn't understand
Any link or advice will be appreciated