Gutenberg is the new “page building” editor that will be included with WordPress 5.0 a few months from now. WordPress 4.9.8 was recently released. It asks you if you want to test the beta version of Gutenberg or if you want to stick with the “Classic” editor (what we all use now). We’re wrapping up Gutenberg support for our themes and intend to have the updates available by the time WordPress 5.0 is released. Until then, we recommend using the classic editor for your live site.