Sql Coding Explanation

public void BindData() 
{ 
SqlCommand cmd; 
cmd = new SqlCommand("sp_GetEmployeeDetails", con); 
cmd.CommandType = CommandType.StoredProcedure; 
cmd.Parameters.Add(new SqlParameter("@roll", SqlDbType.VarChar)).Value = DropDownList1.SelectedValue; 
cmd.Parameters.Add(new SqlParameter("@Name", SqlDbType.VarChar)).Value = TextBox1.Text; 

con.Open(); 
SqlDataAdapter da = new SqlDataAdapter(cmd); 

DataTable dt = new DataTable("Table"); 
da.Fill(dt); 
con.Close(); 
GridView1.DataSource = dt; 
GridView1.DataBind(); 

}