Populating a dropdown box in C#

Here is the simplest 3 tier example I can provide you with.  I am using string return types & only returning strings but you will be returning DataSets or DataReaders & retrieving data from DB.

Create a new ASP.Net Web Application - I called mine "Test3Tier" namespace Test3Tier.

Add a new ClassLibrary project to the Solution.  I called mine "BusinessLayer" - namespace BusinessLayer & I called the Class "BusLayer".

Add another new ClassLibrary project to the Solution. I called mine "DAL" - namespace DAL.  I called the Class "DataLayer".

Add a reference in the BusinessLayer project to the DAL project.  Add a using directive for it to the code (using DAL;)
Add a reference in the Front End project to the Business Layer project. Add a using directive in the codebehind (using BusinessLayer;)

The code in your DataLayer.cs will be something like the following (depending on your namespaces)
//start of code
using System;

namespace DAL
{
      /// <summary>
      /// Summary description for DataLayer.
      /// </summary>
      public class DataLayer
      {
            public DataLayer()
            {
                  //
                  // TODO: Add constructor logic here
                  //
            }

            public string GetData()
            {
                  //This is where you would do your database work.
                  return "From DataLayer"; //Instead of returning a string it would be a DataSet or DataReader
            }
      }
}
//end of code

The code in your BusLayer.cs will be something like the following (depending on your namespaces)
//start of code
using System;
using DAL;

namespace BusinessLayer
{
      /// <summary>
      /// Summary description for BusLayer.
      /// </summary>
      public class BusLayer
      {
            public BusLayer()
            {
                  //
                  // TODO: Add constructor logic here
                  //
            }

            public string GetData()
            {
                  DAL.DataLayer newDataLayerObj = new DataLayer();      
                  return newDataLayerObj.GetData() + "<br>" + " From BusLayer";
            }

      }
}
//end of code


Add a button on the webpage.aspx (In your front end project) called Button1.
add code to the click event for the button so it looks something like this:

      BusinessLayer.BusLayer newBusLayerObj = new BusLayer();
      Response.Write("From WebPage" + "<br>" + newBusLayerObj.GetData());

When you compile & run the webpage will create an instance of BusLayer & run GetData, which will create an instance of DataLayer & run GetData which returns a string to the GetData in BusLayer.
The GetData method in BusLayer then takes this return value from DataLayer & concatenates it with a string & returns it to the WebPage.  
The webpage then displays this using Responce.Write.

Well I already have my existing EmployeeLookUP.Web application.

MOving forward what do recommend is the best way to create the data connection?

Add a database project and reference it?
 Just add two files to the existing project one DB and one sqlprovider class?

Appreciate it.

I downloaded the Microsoft Data Access Application Block.
How do I create a refernce to it.
I right clicked reference in the Employee Look UP application I did not see any Microsoft's Data Access Application Block dll and neither did I see and project I could add to after I borrwed to the Microsofts Data Access Application Block folder that got created in Program Files.