Category problem

Hello there everyone,
thank you for taking your time to look at my problem. I am new to wordpress having a little bit of php knowledge as a beginner and a bit more in CSS side. I am looking at tutorials to understand the wp and build my first custom theme.

At the moment, my problem is that i havent even got an idea how to google for it. I have a main-nav menu on my site where i added a category called ‘Hotels’. When i click on it in the browser directs me to /?cat=6 but nothing shows. My understanding is that i need to show the items from the category. Here comes that i need help. Am i using the single.php to show them? if so, how can i show the items from the category i clicked on?

I found tutorials where you declare what category you want to be shown, but as i want this site dynamic, i would like someone to be kind enough to explain how to?

thanks for your time again,
C.