The Apps for websites section concerns apps that can open websites from within the app this section will let you force apps to open website via browser instead.
The Projecting to this PC section is still in flux, but it looks it will allow you to mirror other devices' displays (PCs, phones, and tablets) on your screen. In the latest Windows Insider Preview Build (Build 14342), there are two new sections in the System tab: Projecting to this PC and Apps for websites.
