Exception Handling at Project Level (3 tier web app)

Question

How to handle exception in ASP.NET web application.

Please say me details at higher level.

 

Suppose, I am working on any big asp.net web application.

Application is simply 3 tier architecture.

1) Presentation Layer

2) Business Layer

3) Database Layer

 

I want handle exception for above 3 layer and save all error log in database with description, error code, error number and other things which are important. 

 

How can we create separate classes for every layer.

 

please tell me in details.

 

Not for demo purpose for big web application.