Newbie question regarding $!model and getParams()

Hi - After several days of playing around with Maverick and Velocity I've
made some progress but still have a few unanswered newbie type questions I'm
hoping someone could take the time to answer.  
 
Question 1 - In general, where and how are the getParams() and setParam()
used?  
If I code 'this.getCtx().setParam("age", "55")'  in the 'perform()' method,
do I have access to this in the 'transform', and more specifically, how do I
reference it in VLT?
 
Is it referenced by $model.getParams()  or  $model.getParams("age")  or
$response.getParams() .... etc.  I've tried several permutations but just
can't figure it out.
 
Question 2 - I've seen in the opt-velocity friendbook example several
references to "$!model.xxx".  What is the bang (ie '!')  for? and why is it
used?
 
Thanks, Bob
 
PS  Feel free to point me to the documentation if I've missed it in there.