How to show the post announcement on the main page?

Question

WordPress

Hello.
WordPress Twenty Fifteen Theme:
I can't announce a post on the main and headings.
By default, the topic is configured as follows: all posts are shown in full.

I changed the value of the_content to the_excerpt in the content.php file, almost done, but when you go to the post page, everything remains the same - “read more”.

Answer 1

It is possible like this:

if ( is_single() ) {
  the_content();
} else {
  the_excerpt();
}

It is advisable to create a child theme, copy the content.php file into it and make changes to it so that the changes are not overwritten when the theme is updated