# Get the reference to the "vms" service:
vms_service = connection.system_service.vms_service

# Find the virtual machine:
vm = vms_service.list(search: 'name=myvm')[0]

# Locate the service that manages the virtual machine, as that is where
# the action methods are defined:
vm_service = vms_service.vm_service(vm.id)

# Call the "start" method of the service to start it:
vm_service.start

# Wait until the virtual machine status is UP:
loop do
  sleep(5)
  vm = vm_service.get
  break if vm.status == OvirtSDK4::VmStatus::UP
end