I was trying to clean up my site the other day, and I hadn't even realized that blogger's new posting editor allows you to condense your posts on the main page and click on "Read More" to read the rest of the article. It is a fabulous way for your readers to be able to find what they are looking for more easily, with out having to scroll down long articles.
The new tool offered is called the Insert Jump Break tool. This is what it looks like:
If you do not see this toolbar, it is probably because you are still using the old editor. To get the new editor, go to your "Settings" tab and "Basic".
Scroll to the bottom and make sure that "Updated Editor" is selected.
And there you have it Condensed Summary Posts that are expandable!