Change Layout of how blog entries are displayed on blog landing page

Hi,

I am working on this site: https://myoga.com/newsite/

I am using the Twenty Twelve theme.

I would like to change the way blog entries display on this page: https://myoga.com/newsite/blog/

I would like them to display the featured image, title, a bit of the text (but not the full entry) and then the sharing buttons below.

I know I have done this (possibly with other themes) in the past, but cannot seem to find the settings for it in the Twenty Twelve theme. Perhaps it is something I need to customize?

If you can offer any help I would so greatly appreciate it. Thank you!

Brittany