My friend Paul Long from Netmon Team recorded a series of videos that will allow you to better understand how Netmon works and how to use it. Check it out here:

 

UI Overview Part 1

 

 

UI Overview Part 2

 

 

Capturing with the UI

 

 

Capturing with NmCap

 

 

Filtering

 

 

Conversation Tree

 

 

Creating a New Parser