Google Tag Manager tags explained

Can someone explain the Google Tag Manager (container) code and help me learn the following:

<script>
(
function(w,d,s,l,i){
w[l] = w[l] || [];
w[l].push({'gtm.start': new Date().getTime(), event:'gtm.js'});
var f = d.getElementsByTagName(s)[0],
var j = d.createElement(s),
var dl = l! = 'dataLayer' ? '&l=' +l : '' ;
j.async = true;
j.src = '//www.googletagmanager.com/gtm.js?id='+i+dl;
f.parentNode.insertBefore(j,f);
}
)
(window, document,'script','dataLayer','GTM-xxxxx');
</script>

String:

1. Why start with an opening bracket? ("(function...") What are the 5 arguments to wdsli?

   2. Set the "L" element of the "w" array to itself or to an empty array.
   3. Pushes an object into the last position of the w array, 2 properties and 2 values.
   4. Set var f to the first element of the s array.
   5. Set var j to element s (but what is "d."?).
   6. Asynchronous loading is true, all clear here.
   7. Javascript sources, all clear here.
   8. Absolutely no idea what this does, something to do with the DOM?
   9. Does this seem like a function call? The first letter in the function prototype seems to correspond to these parenthesized parameters?

Also, if the dataLayer doesn't already exist in the html page, how will this code generate the dataLayer before itself? I know it has to come before this container code, otherwise GTM can't use the data in the dataLayer.

Totally lost here, so any help is appreciated!

EDIT 2: I completely forgot one line, and the one I had the most trouble understanding:

var dl = l != 'dataLayer' ? '&l=' +l : '' ;

"If variable dl(dataLayer?) is set to value l(dataLayer?), but "dataLayer" does not exist, then (somewhat oddly) + l (add dataLayer) else empty/empty string

Thanks!