How to Save
The editor will save as you go, so there is no need to do anything special to save the changes you make. It is saved for you automatically. You can just close out of the editor and come back when you're ready -- all of the work you previously created will be there waiting for you.
There are a few exceptions where this is not true, and you will need to save your changes. You can save a blog post to work on later (before Publishing it), be sure to click the Save to Draft button at the top of the post. When you make changes on the Settings tab of the editor, you will also need to Save your changes.