Hiding subpages in navigation?

Hi, I have been googling to try and figure this out myself, but I can’t seem to. How can I get the subpages to hide in my main navigation? I’m a writer so my portfolio is going to be full of things and I don’t want all of my portfolio things listed in my main navigation, you know? I had a layout ages ago that didn’t list the subpages, but I can no longer find it (and I forget the name) so I’m not entirely sure how it was achieved.

If any of you have ideas, that would be great!