How do I download Chap. 2 Ihave Chap. 1 in my computer. Or is it automatic.

It is my understanding that you:

Open Steam.
Open The Raven game.
It will then automatically download Chapter 2.

Play a new game directly and select Chapter 2.

Alternatively, if you downloaded it from anywhere other than Steam, when you start up the game it will advise you if there is a new patch available. Click on the patch button to download and install. (There may be more than one patch.) Then start New Game and select Chapter 2.