Purpose of hole in Valve cover?

[MoparGuy]

When I bought my car I had a mopar performance set of valve covers.  The Mopar Performance passenger side valve cover had a plug but the old passenger valve cover that I'm putting on has a hole similar to the one in the pic below.  My driver side valve cover has the oil filler cap & is connected to my air breather.   My first question is, What's the purpose of this hole on the passenger side valve cover?  Second question is what do I need to buy?  Where? The one in the pic looks like it's hooked up to the carb??

They say no question is a dumb one, so please bare with me.  This is all a learning experience for me!
In advance any & all help would be appreciated!
Enjoy your Charger this year,
MoparGuy

[WingCharger]

It is part of the breather system. I think that you need it...

[John_Kunkel]

The item in the pic is the Positive Crankcase Ventilation (PCV) valve, it hooks to a vacuum port on the carb and draws vapors from the crankcase into the engine to be burned off.

The valve can be installed in a closed system that draws no outside air or on an open system that draws fresh air from the air cleaner.