You edit the content of pages and articles using text and html codes.
Text vs. visual editor
When working in a text editor , all inserted content is displayed in html format. To see what the embedded content will look like when creating a post, switch to the visual editor in the upper right corner of the editor. The codes will not be displayed in the visual editor as well as on the website. Only embedded content will be displayed.
Text editor when creating a page
You can find this editor on the article creation or editing page. If you have at least a basic knowledge of html, it can be very beneficial for you. Thanks to it, you can see every feature and embedded content in posts. You also have more control over individual paragraph breaks and the like.
You can read more about writing articles at codex.wordpress.org .