The process of an app installed into iOS device?

For example, when I install an app X.app from app store.

1. 
   

   search and download x.app from app store.

   
   


2. 
   

   iOS install x.app into somewhere in /var/mobile/Applications/XXXXX ??

   
   


3. 
   

   iOS add a new entry in keychain

   
   


4. 
   

   others?

   
   

Is this sufficient? Anything missing?