You can extract specific text using split() method in PowerShell.
$txt = "www.google.com"
$txt.Split(".")
Split() return an Array and the first element is www. So if you want to return google write the following:
$y = $txt.Split(".")[1]
Another example
$email = "mail@gmail.com"
$x = $email.Split("@")
$domain = $x[1]
$domain = $domain.Split(".")[0]
Write-Host "email: " $email
Write-Host "Domain: " $domain
Output:
email: mail@gmail.com
Domain: gmail