Pages within a category to be posted in collapsible mode

Currently I have a widget to the left bar so user selects a category and sees all posts under this category. The problem is that all posts are displayed fully expanded. Is there any way to set this so page displays only the posts\ titles?. So when I click the title the pages displays the full content of this title? Thank you.

The page I need help with: [log in to see the link]