"Invoke-Sqlcmd" and "Install-Module" not available?

SQL-Query.cs

using System;
using System.Data.SqlClient;

namespace RKTMB {
  class Program
    {
        private static SqlConnection cnn;
        public static void FetchAllNames()
        {
            string connectionString = null;
            connectionString = @"Server=sql-server.rktmb.org\dev;Database=Customers;User ID=RKTMB\MR01;Password=Madagasikara;Trusted_Connection=true;";
            cnn = new SqlConnection(connectionString);
            try
            {
                cnn.Open();
                SqlCommand command = new SqlCommand("SELECT DISTINCT [Name] FROM [Customers].[dbo].[Customers]", cnn);
                SqlDataReader reader = command.ExecuteReader();
                while (reader.Read())
                {
                    Console.WriteLine("This is hat I read:\t{0}", reader.GetString(0));
                }
                cnn.Close();
                Console.ReadLine();
            }
            catch (Exception ex)
            {
                Console.WriteLine("Exception");
                Console.ReadLine();
            }
        }
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
            FetchAllNames();
        }
    }
}