Thank you for the link you posted. There are two methods to split a post into a summary or excerpt, which is achieved from how the theme’s content template file is coded. You can have a content summary which is determined from the point where the author inserts a “read more” tag into the post, or an excerpt where a specific character count determines a fixed summary of text. Either one provides a short summary with the ability to proceed to the full article.
Is this what you were wanting? If so, the content.php file will require modifying.