What is a player PC and why is it needed?
A player PC is a Windows-based PC that is connected to your screen/display. On the player PC the FrontFace Player App is installed.
Without a player PC, you cannot use FrontFace. Some screens can be directly connected to a local network or the Internet (aka SmartTVs) but this is not sufficient to run FrontFace. - An exception is TVs with integrated Android TV: Since there is also an Android version available (with limited functionality, though), you can also install FrontFace on Android devices.
Apart from common desktop/notebook PCs, you can also use compact mini PCs (i.e. a small form factor PC, often also called a "thin client") or stick PCs that can be easily mounted directly behind the screen.