So ...

There are three different ways ...

1. The default excerpt metabox

By default, you have an excerpt meta box below your post editor. If you can't see it, you'll have to click on the "Screen Options" tab on the top right and then check the "Excerpt" checkbox:

The excerpt meta box will be displayed below your post editor and you can add any custom text in this box, in order to use it as the excerpt for the given post:

The problem is that MANY themes will simply ignore these excerpts ... In which case you'll have to edit a bunch of theme template files like home.php, category.php, archive.php, etc. And that would require strong coding skills ...

2. Using the "Read More" tag

Another common way to create excerpts is by using the "Read More" tag.

All you have to do, is to place your cursor in the post editor to the point where you want to break the post and then click on the "Insert read More tag" button:

Usually, this method works, beacuse most themes are properly configured to handle and display the Read More tag ...

However, if your theme isn’t, then don’t worry ... There is another bulletproof way ...

Let's check it out ...