Navigation/sub-navigation

Hi There

I have 5 main pages for my site.

Most of them will require a side navigation with sub pages.

When I try to add an additional page or sub page it wants to appear at the top of the page (and also in the footer I made).

Is there any way to prevent this and instead put it into a side navigation?

I tried to customise the side bar but when I try to make a new “menu” it messes up my main nav.

Any ideas?

Cheers for all your help!