It’s not a “pack”, it’s a bottle of liquid. “Diesel exhaust fluid” is the generic term, Adblue is a trademarked name you’ll hear. The tank for DEF should be topped off during routine maintenance.
You need a diagnostic computer hooked up to the car to check levels, apparently - there is no dipstick on the (rather large) DEF tank. So for most drivers this is not a DIY operation like checking your oil level.
Here’s a video of a Passat being filled.
http://youtu.be/1h9hWlvg6sM
They talk about using VCDS, a DIY diagnostic software and cable setup, to check level. If you’re a serious DIY mechanic these days, you have to have it to work on modern cars. I’ve had the setup for around 10 years now.
IMPORTANT!
The 2.0 TDI in the Golf does not use Adblue DEF. So scratch any reference to that.
What’s confusing is that the Passat 2.0 TDI DOES use Adblue.
I got to reading up on things at myturbodiesel.com, and learned this.
Also, chickensoup, if someone hasn’t posted this link from there in this thread already, you really need to see this:
2010-2013 VW Golf TDI FAQ, forum, and buying checklist
http://www.myturbodiesel.com/1000q/a6/2010-2011-VW-Golf-TDI-buyers-checklist.htm
Tons of useful information for you there.