Need urgent help with Text Wrap in Theme

I have my technology blog hosted at https://www.doubleclickblog.com. Though things seem pretty smooth with WordPress, being a novice, I need to display only a few lines rather than the complete post. I have tried Settings>Reading and selecting “For each article in a feed, show Summary” but nothing helps. I would highly appreciate if someone can help me with this. Secondly a bit off topic, I want to know how to display thumbnails in the post which open in a new window when clicked. All help would be highly appreciated.

A WP Newbie,

Sam