How can I share something on my Facebook group?

How can I post something on my Facebook group and where can I find the group id?

$("#group").click(function() {
  FB.api("/{group-id}/feed", "POST", {
    "message": "This is a test message"
  }, function(response) {
    if (response && !response.error) {
      console.log('User shared the message')
    } else {
      console.log('User did not shared the message')
    }
  });
));