In a nutshell, Gutenberg is a brand new editor for the WordPress platform. It will radically change the way you create posts, pages, products, and just about everything else on your site.
Many of you are probably wondering, will Gutenberg be optional? When they roll out Gutenberg officially into WordPress core 5.0 and all the core updates thereafter, you won’t be able to turn it off, as this will become the official editor for your WordPress site.
There is, however, a free plugin called Classic Editor which you can use to restore the old post editor, but use this as a means to an end.
We also recommend checking out this post we created back in June of 2018 on Gutenberg is Alive which might answer any additional questions you might have.