void Main()
{
  var users = new List<User>();
  using (var connection = new SqlConnection("Server=localhost;Database=TestDb;Trusted_Connection=True;"))
  {
    connection.Open();
    
    using (var command = new SqlCommand("SELECT UserId, FirstName, LastName FROM dbo.Users", connection))
    {
      using (var reader = command.ExecuteReader())
      {
        while (reader.Read())
        {
          var user = new User();
          user.UserId = (int)reader["UserId"];
          user.FirstName = (string)reader["FirstName"];
          user.LastName = (string)reader["LastName"];
          users.Add(user);
        }
      }
    }
    
    connection.Close();
  }
  
  foreach (var user in users)
  {
    Console.WriteLine("UserId: {0}", user.UserId);
    Console.WriteLine("FirstName: {0}", user.FirstName);
    Console.WriteLine("LastName: {0}", user.LastName);
  }
}

public class User
{
  public int UserId { get; set; }
  public string FirstName { get; set; }
  public string LastName { get; set; }
}