Global Content is a way for you to create widgets that you will then later be able to use on other pages via the Global Content Widget.
When you have created a widget here it will work as a template in the future, so that you will only have to set it up once, saving you a lot of time in the future.
Setting your widgets up with this feature ensures that every time you make a new page, you can get the same design on each page. All you will need to do is add them in the Global Content widget, making it straight forward to keep the same design on all of your pages.
Click the three dots to the right of "Content". Select the Global Content Holder, give it a name and then save and publish.
You can also add more Global Content Holders under your first one if you wish to create a deeper structure.
You can add one or more widgets on each Global Content node. You can also nest Global Content nodes by adding the Global Content widget here.
To display the Global Content on your site, use the Global Content Widget.