Mapping posts to pages

Hi,

I try to understand how my 3 posts at the startpage are mapped.
Have a look at this website: https://www.lld-eder.de
You see the 3 images/posts, and if you click on each of them, then always the same page is linked.
How can I have 3 different pages?
At the navigation on top you see my 3 categories again (Hochzeit/Portraits/Sonstiges) and there the pages are working.
Do I integrate 3 different php files for these pages?

I’m very happy about helpful comments!

Thanks!