Q: can anyone explain the process of gifting an app?

Can anyone explain what happens when you gift an app?  I tried to gift "Where's My Water" to my son.  How does he retrieve the gift? He tried to go to the App Store and download it (I thought it might already be marked "Purchased") but it wasn't.  Does he get an e-mail with a retrieval code?  His e-mail is set up to only get mail from certain people.  What address would we need to add to his address book so the e-mail will go through?  How do I get the confirmation resent to him?

Thanks!

Lynne