In December 2018, WordPress released version 5.0 which launched a new editor called 'Gutenberg'. The focus of Gutenberg is to create a new post and page editing experience that makes it easy for anyone to create rich post layouts. You can view more information at the following link:
Should I continue to learn Gutenberg or revert to the old editor?
Gutenberg is a different editing experience and some users may find it confusing at first. Long term, this will be the only editor for WordPress, so you will eventually need to learn to use it.
In addition, your site might use a theme or a plugin which doesn't work with the new Gutenberg editor, so you will want to consider an edit or a redesign for your site sometime in the next year or so.
However, in the meantime you still have the option to revert to the classic editor so you can continue to work on your site.
Reverting to the old classic WordPress editor
WordPress has created a plugin that allows you to revert to the old classic editor.
View the following article for instructions on how to install and activate a plugin: