Beginner's question: Using Parameters on SqlCommand

Im teaching myself how to use a strongly typed dataset in C#.  I want to do this by hand, rather than letting a wizard build it all for me  you dont know something if you dont know how to do it by hand.

The code below has two problems, which probably have the same cause:
1)  After building the other commands via SqlCommandBuilder, the SqlDataAdapter shows null Insert, Delete, and Update. commands.
2)  When the code executes da.Fill(ds), I get an exception saying

The parameterized query '(@Col1 int,@Col2 int)Select @Col1, @Col2 from TestTable' expects the parameter '@Col1', which was not supplied.

What am I doing wrong?

using System;
using System.Data;
using System.Data.SqlClient;

namespace QuickSQL {
   class Program {
      static void Main(string[] args) {
         SqlConnection conn = new SqlConnection(@"Server=(local)\SQLEXPRESS;Initial Catalog=;Integrated Security=SSPI");
         conn.Open();
         SqlCommand cmd0 = new SqlCommand("Use Test",conn);
         cmd0.ExecuteNonQuery();
         SqlCommand cmd1 = new SqlCommand("Create Table TestTable (Col1 Int Primary Key, Col2 Int)",conn);
         cmd1.ExecuteNonQuery();
         
         SqlDataAdapter da = new SqlDataAdapter("Select @Col1, @Col2 from TestTable",conn);
         da.SelectCommand.Parameters.Add("@Col1", SqlDbType.Int);
         da.SelectCommand.Parameters.Add("@Col2", SqlDbType.Int);
         SqlCommandBuilder builderTarget = new SqlCommandBuilder(da);
         
         DataSet ds = new DataSet();
         ds.Clear(); da.Fill(ds); // Exception thrown on da.Fill(ds)
         conn.Close();
      }
   }
}

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