3-Tier

1. Create a simple web-site and use SQL DataSource directly in the aspx page, create a GridView and populate some data
   
2. Now remove the SQL Datasource and create a class call it DAL which does the SQL calling and get the DataSet. Sonsume that class's method in aspx to do DataBind
   
3. Now try to create a Business Entity and hydrate the Business Entity in the DAL and pass it to the aspx using a dummy Business Layer Class
   

Kudos you've created a 3-Tier Application