Google Tag manager has been around for while in fact I remember writing an article some time back about its entrance onto the scene. Well! its come a long way since then and now if you are an online marketer and haven't got your head around this thing - hint: START NOW! Put simply, Google tag manager is a digital marketers best friend. To describe it's functionality briefly, it basically creates a window, or container as they call it, onto a site - that allows anyone within the designated tag manager account to insert ANY CODE THEY WANT. Scary? a little I suppose, however the ability to unobtrusively manage "tags" in a portal away for the site - is SOOOOO powerful. Below are 3 main aspects that make up google tag manager.
A tag manager tag
A tag manager Rule
As the name suggests, the rule concept determines where the tag itself is aloud to fire on site. An example of this might be you have installed a tag with live chat code however you only want that live chat code to appear on product landing pages and not the checkout - you simply create a rule that prevents the tag from being fired on these pages. You can you Regex (regular expressions) or simply leverage their string filters e.g url: contains, equals etc
Macros are little programmable snippets within GTM that allow you create more advanced rules. These rules generally involve dynamic data that needs to be passed from an element or variable with the page's DOM.
In conclusion, I've always been a fan of this tool and being a developer at heart I understand how powerful this thing really is when your looking to leverage it in the online marketing space. Sign up, get around it and get tagging.