Assigning new pages to different sections of the site are done within the resource itself under Template Variables.
However, adding sections to the Top Navigation Bar requires manually editing a Chunks within MODX.
To add a new Admissions Program to the Admissions section, for example, Navigate to Elements, select Chunks, then Navigation, and select the nav_admissions chunk to manually add the page. Be sure to use Resource IDs in place of the URL.