Only title in the post overview

Hello I am just a beginner, so please help me with the following problem in the Catch Base Pro theme: The listing of my posts only shows the title or the excerpt without the image. It looks like that example: http://bremer-ukulelenorchester.de/Archive/category/aktuell I would prefer a view like this: http://anne-achner.de/blog/?cat=3 How can I achieve it? Please help! Thank you!!!!