Re-use bits of code in multiple locations but edit in one.

Create a folder called "template-parts" in your theme

Inside that folder, add a PHP file called "content-example.php"

To display this, use the following snippet
<?php get_template_part('template-parts/content','example'); ?>

If your file name does not contain a hypen, for example something like "team.php" - then the snippet changes to:
<?php get_template_part('template-parts/team'); ?>

Inside the file, add the following code:

* The template part for displaying content example

<p>Content here</p>