Change the layout of latest content in index.php

Hello.

I want to change the way my index/home directory displays the latest content. I want it to look less like blog style and so I want to have small boxes aligned next to each other (maybe 3-4 per line) like many premium themes have it, too.
I tried to google around and also read to many threads here, but thus far I wasn’t able to figure it out.
Currently I only managed to resize the content box to be around 250px, but the single post boxes are still below each other and not next to each other.

Any ideas?

Thanks a lot in advance! ??