ET Headquarters adds a flexible character customization system to Wolfenstein Enemy Territory. It also adds gameplay changes and rebalances class mechanics. Its core gameplay remains close to vanilla ET.
Official ET Headquarters Standard Character Customization Pack. This is the WW2 themed item pack. It contains 10 body- and helmetskins, 5 rankskins and headaccessoirs, and 30 faceskins. Version: alpha 1.0
Is this necessary for the game? I don't know...
It's optional. So no, it is not necessary.
If you want to use it, download it, and place it in hq folder. You must place it in server first, so clients can download it.
You can also make your own cc pack. This is just an example. Take a look in manual if you want to define your own cc pack.
I see...thanks!