There are lots of reasons why you might want to exclude pages from the navbar. You can do so if you want to clean your navigation up and put subpages on the sidebar instead, or maybe you just want a “hidden” page on your website to send staff members or family to or whatever. I always add the Exclude Pages Plugin into my themes and this is how you use that.
Go to the page you want and scroll to the bottom right hand side and look for “include pages.” Uncheck the box. Save changes. That’s it!