How to insert a “Read More” button?

New Editor (since WP version 5.0)

At the point in your text where you want to add the “read more” button click the “+” icon, locate the “more” block and add it.
The content above the “more” block will be your post’s excerpt and the content you add below the “more” block will now be visible only when the “read more” button is clicked.

Classic Editor

If you are using visual editor then you can add it by clicking on this icon above the editor window.

If you are using text editor you can insert a “Read More” button into posts by simply adding <!--more--> tag inside the post text editor where you want the button to appear. You can also add it by clicking on the “more” button above the text editor window.