Editing your old blog posts with the new blocks editor

Your old (pre-block editor) blog posts will have all of your content in one big block. 
To turn on the block editor, you’ll need to click in the top right corner of your editor.
Sometimes you need to switch back and fourth between the editors.
With anything new, a bit of experimentation will help you figure out the best time to use blocks, and when to use your old editor.