Suppose you have adropdownlist "drpCities" you want to show city list using this dropdownlist. Here is the sample code:
SqlCommand cmd = default(SqlCommand);
SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["Callregister_connectionstring"].ConnectionString);
con.Open();
cmd = new SqlCommand("Select cityId,cityName from City order by cityName", con);
cmd.CommandType = CommandType.Text;
DataTable dt = new DataTable();
SqlDataAdapter da = new SqlDataAdapter();
da.SelectCommand = cmd;
da.Fill(dt);
drpCities.DataSource = dt.DefaultView;
drpCities.DataTextField = "cityName";
drpCities.DataValueField = "cityId";
drpCities.DataBind();