Automattic recently updated WordPress to version 5.0 and at the same time added the Gutenberg (block) editor as the default content editor.
If you are not familiar with the block editor it is possible to continue to use the Classic editor that you are used to.
Just install and activate the Classic Editor plugin from here:
You can learn more about the block editor here: https://gogutenberg.com/
Get in touch if you have any questions or problems