To start and stop machines using vagrant, change your directory to where your Vagrantfile is. Use vagrant up to start and vagrant halt to stop the machines.
cd \repos\certified-kubernetes-administrator-course\kubeadm-clusters\virtualbox
vagrant up
Bringing machine 'controlplane' up with 'virtualbox' provider...
Bringing machine 'node01' up with 'virtualbox' provider...
Bringing machine 'node02' up with 'virtualbox' provider...
# Large logs removed...
vagrant halt
==> node02: Attempting graceful shutdown of VM...
==> node01: Attempting graceful shutdown of VM...
==> controlplane: Attempting graceful shutdown of VM...
controlplane: Guest communication could not be established! This is usually because
controlplane: SSH is not running, the authentication information was changed,
controlplane: or some other networking issue. Vagrant will force halt, if
controlplane: capable.
==> controlplane: Forcing shutdown of VM...