Formatting the way posts are displayed on the main page

Hello,

So I’ve recently been setup WordPress to use as a CMS. No issues with the installation or anything.

However I’m at a bit of a loss on how to change the way the list of Posts is displayed on the main-index.php page.

Basically rather than having the entire post in all it’s glory showing up I’d like a summary, with a thumbnail of the first image in the post left-aligned to the summary.

I’m terrible at explaining these things so I made a quick diagram, the top is how WP does it by default, the bottom is what I’m aiming for:

diagram

I had a gander around and figure I need to use the_excerpt() though not entire sure on how I go about that and subsequently editting the CSS it uses.

Any help would be appreciated.