The easiest way to understand structured data is to think about the different types of forms you fill out:
Rental Application
Motor Vehicle Registration
Post Office Shipping Label
All of these items are similar in the fact that they are formatted appropriately for the type of data that they contain.
Let's use a shipping label for our example, because it's simple and fairly universal.
No matter who comes in to send a package at the post office, each person will be presented a form and they need to fill out the required information in the way the form requests it.
You're probably thinking that the answer is pretty obvious, right? We do it, for a couple of reasons:
So that whoever is doing the sorting at the post office doesn't have to waste time figuring out how to route the packages
So that whoever is delivering the packages doesn't have to waste time finding the name of who to deliver it to
In short, it's to increase clarity and make things easier to work with, which, in turn, increases efficiency and makes life easier.
You might be wondering what all of this has to do with Drupal.
The answer is simple. It has everything to do with Drupal. In fact, the ability to create structured content is one of the main reasons why Drupal is used. To be able to deliver content in a lean and clean manner, we want to structure as much of it as possible.
So now would be a good time to watch one of my favorite videos from renowned content strategist Karen McGrane. Here's her keynote presentation at Drupalcon Portland, back in May of 2013. Pay close attention as McGrane highlights exactly why structured content is so necessary for adaptive content (which means that it can easily move from many different platforms, such as from the Web to your mobile device).
If you would prefer, you can also read a transcript and view the slides from the presentation.
Now that we understand a little about why structured content is so important, let's get to work figuring out how to actually structure it!