Read more?

Hello everbyody!

I have a small problem with wordpress. I am using the Dark theme from Bartelme and I cannot make wordpress cut every post on the front page (here is my website) and instead add a “read more” link so that my visitors have to click on the link to read the full post.

I know that I have to somehow use the summary feature of wordpress but I cannot figure out how!

Can someone please help me how to add this link?
Thank you very much!