Typically how it works is if you have a page of:
and alias setup on that page (above) of:
Kentico will by default, take you to /page-1/sub-page and display the content of /page-1/sub.
There is a setting in Settings>URLs & SEO where you can redirect aliases to their main URL, which would mean when someone goes to /page-1/sub-page, it would automatically redirect (302) to /page-1/sub.
Not sure if this answers your question or not but hope it helps.