Link to sub pages

Let’s say that I am now creating a multi page mock up for my full stack project.

I know that in React or Vue you can create different component and put those into the specific pages you want.

For example, in the layout below, if I use a framework like react, I can make the left catagory panel to appear on every page I have. Or, I can make it only appear on the index page.

Right now my question is this : how do I make the middle part that is within the red border only appears in the 1st sub catagory of the page? Right now it is on the index page. Do I have to create another page? Like or something? Then put it inside the tag?