About Bullet Collision Detection & Physics Library

Bullet API
I found the API from Bullet Document is not useful for us;
It only simply show the prototype of function without a little explaination.It is not friendly to us who is noob for Physics Library;

So,Is there some friendly doc for me ,Or some article,Show me a link please…
I just want to know what is the target of certain function;
void btCompoundShape::addChildShape ( const btTransform & localTransform, btCollisionShape * shape )
I can’t understant it,How to use it to compose two shape…,Because It only show a prototype …