For the ASP.net You can create following layers
1) DAL Layer: Which is used for the database. All the DB related actions should be performed here only, no where else DB should accessed.
2) BusinessLayer : where you can define the business logic.
3) Presentation Layer: UI display for the user.
You can go through following link for getting basic idea of layers in .net application
Three Layer Architecture in C# .NET[
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