electromagnetism - Why group velocity represents energy or information transmission? What relation between phase velocity and special relativity

I have two question,

1. 
   

   why group velocity represents energy or information transmission?

   
   


2. 
   

   what is the relation between phase velocity and Special relativity: why can it exceed C without violation of SR?

   
   

I didn't take any classes in special relativity or information theory or quantum mechanics, my background only contains

1. 
   

   general physics (basic knowledge about Special relativity)

   
   


2. 
   

   electromagnetism

   
   


3. 
   

   signals and systems (basic knowledge about signal transmission),

   
   
   

so please reply in a simple and easy way.