In situations where the article is featured on the homepage or listed in the summary page of a blog, typically you only want the first paragraph to display and then followed with a "Read More call-to-action link" teasing the visitor to click through to the full article.
Where upon clicking on the "Read More" the full article is displayed.
Required Steps
1.) Add a new article or Edit an existing article.
2.) Type your article into the editor panel.
Warning:
Do not paste content directly from Microsoft Word (or any other word processor) into the editor here. Hidden tags and unwanted information is
transferred into the article which may be detrimental for SEO rankings.
Refer to the Content Preparation Instructions for further explanation.
2.) After the first paragraph or where you desire the "Read More" call-to-action link, place your cursor at that position. In this example, the cursor is placed after the first paragraph.
3.) Click the "Read More" button at the bottom of the editor.
4.) A squiggly red line will appear after the first paragraph (or wherever you had place your cursor.)
5.) Save the Article
6.) Visit the public side of the web site, refresh your browser, and the "Read More" call-to-action link will appear.
Official Joomla Documentation
Splitting an Article into an introduction with a link to read more
https://docs.joomla.org/Splitting_an_Article_into_an_introduction_with_a_link_to_read_more