How can I add notifications/alerts? 

For example:

User 1 adds User 2 as a friend.

User 2 gets an "Alert"

User 2 confirms friend request.

User 1 doesn't get any type of alert/notification.

Example 2:

User 1 posts on User 2 wall.

User 2 doesn't get a notification, but does get an email.

How can all this be turned into alerts, and/or emails? 

I hope I'm missing something simple here.. This feature is how sites such as Facebook socially expand as quickly as they do, navigating users through alerts and links, making it easy to stay in touch, etc. 

I literally want to duplicate the alert/notification features similar to Facebook. A Notification/Alert should show up from wall posts, replies, friend adds, friend accepts, etc.

Please give me any advice possible.

Thanks!

- Patrick