page – show post excerpts

Hi,
the homepage is working great so far, but the individual pages, which i linked to categories (default page template) give me this trouble: there is page text as expected, but then i only see category posts titles.
Is it possible to show title+excerpts+thumbnails instead of just the titles on the page? I tried to change the code, but got lost…
It would be also great to add category background to the post title but that would be only bonus :).

Thank you,
aliiva