This is a very simple tip, but judging by the number of queries on the Product Forums, it should prove helpful. Blogger is a free blogging service by Google. Like WordPress, they allow you to run hosted blogs on the blogger.com domain, and they also allow you to modify the HTML source. This, of course, means that you can add the Google Tag Manager code to the HTML template, if you wish (and why wouldn't you!
First of all, I'm sorry for the wacky title. Sometimes I just want to amuse myself. Nevertheless, this post is about the Google Tag Manager container snippet. There's nothing secretive about it, but I'm betting many people have no clue what the snippet really does. That's the revelatory part. If you've never wondered what the snippet does, then shame on you! Remember, you own your page template. It's yours. Any code that you write there is your responsibility.