Thank you very much for your answer.

Is it basically possible to change the display-settings of the post so that not only the “excerpt length” is displayed but rather the full content of the text, so the visiter wouldn’t need to click on the respective post to see the entire content but he would see all of it directly on the front page?

Secondly if i put in an image in the post it won’t be displayed, only if it is a featured image but not an usual added image to the post.
Is it here also possible to just add usual images in the post and show them on the front page without the need to use the “featured image” option?