I will try to explain:
1. if you include the collapse element as part of your content then wherever that content is displayed, the shortcode magic comes with it. Regardless of which page the content is being displayed: is_home() or is_single() or is_page() will always display the content WITH the short code.
2. if you included the collapse element as part of your template then you can control where the content will be collapsed, and where it will just be pure, uncollapsed content goodness.
On your site, you would want to make the intro text (the part that is never collapsed) the post's excerpt. The content that is collapsed (on your homepage) but not collapsed when the user visits the actual article--could then be controlled within the templates used for your
single.php template files (or whatever they are called in your theme).
If this is going over your head, you might want to contact your theme developer, or someone that can help you with customizing your theme.
Hope that helped more than confused you.
To sum up:
The loop on the home page template would use do_shortcode and might look something like
do_shortcode('[expand title="read more" swaptitle="read less"]'.get_the_content().'[/expand]');
and the loop on the single article template more like: