Dear friends,
Sorry for the newbie question:
"set your “profile” in Lightroom to “Negative Lab v2.1”
- what does it mean?
Thank you!
Negative Lab Pro uses its own camera profiles. When NLP is installed, these profiles are copied to a place that Lightroom (and NLP) can see. NLP will activate one of these profiles before converting.
When you use NLP, Lightroom will show that the NLP-Profile is active:
Please note that the profile advertises as v2.0, not v2.1.
On a Mac, these profiles should have been placed where 
is
MyDisk/Users/MyHomeFolder/Library/Application Support/Adobe/CameraRaw/CameraProfiles/
(replace the text in italic by the names of your disk and home folder respectively)