Sounds like you read a magazine article but don't really understand what you're doing.
1 - you write code to call the DAL and check the return values.
2 - I don't know. I would expect that the Customer class would have a constructor that creates a new object and stores it in the DB. But, your business needs are up to you
3 - The UI can call the DAL directly if all it wants is to get back a collection of objects from the DB.
coommark wrote: as i have never worked on this type of layered architecture.
Well, it's really common sense. Make sure the layers do not rely on each other overly, and keep all data access in the DAL, and all business logic in the BLL.