Hi,
You will need something like this :
import-module DataOntap
$ControllerPassword = ConvertTo-SecureString -String "your password" -AsPlainText -force
$ControllerCredential = New-Object System.Management.Automation.PsCredential("root",$ControllerPassword)
$filer = "your filer"
connect-NaController $filer -Credential $ControllerCredential | out-null
  $aggregate = get-naefficiency -aggregate *
  $aggregate_used = ($aggregate | measure-object -property Used -sum).sum/1024/1024/1024
  $aggregate_free = [Math]::Round(($aggregate | measure-object -property Free -sum).sum/1024/1024/1024,0)
  $aggregate_capacity = [Math]::Round(($aggregate | measure-object -property Capacity -sum).sum/1024/1024/1024,0)
you can then play with the variables to achieve whatever statistics you would like to have printed.