Creating a site within a site

If original domain is example.org, you can create site within site in this patterns :

example.org/site/
example.org/site/within/

site.example.org
site.within.example.org

Almost like having a “new” website.

100% warranty. Full real websites.

but I want to create a page to put in my navigation bar but then have different pages go off that page only

Possible.

Am I making any sense? Do I need two menus?

Difficult to say yes !
But you can have one or two number of menus as you like.

In future : Draw with pen and paper and scan it, upload somewhere when you can not explain something because of unknown terminologies.