How to make post grid

Hello.
I have made the menu which consists of categories because I wanted “pages” with posts in it. Now I want to customize how posts will look in those “pages”. I found that there are plugins which could help, but there are shortcodes which I need to put in a page, but I can’t do it because I don’t have pages, but I have categories.
Can someone help me? Is there any alternative, how I can easy create post grid?
Thanks.