Hi
There is no tutorial yet on using the WYSIWYG Layout Editor. The video tutorial is ongoing. For the mean time you can read on how to use the Page class in the Docs of Layout Editor.
Click the code icon to Open the Code Editor.
You can the see the code of the current page class. Click the second icon from the right to Open the Page class documentation. The third icon from the right is the UI Components documentation. You can also type your code in the code editor if you want to edit the code directly in Layout extension.
This is the documentation of the Page class. You can refer to this Docs when you have problem related to Layout pages in the WYSIWYG Editor.
Regards