Opportunities and Custom Fields

Having problems linking an opportunity to a customer and assiging a value to a customer field that is associated with an opportunity. Here is what I have tried in C#

using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Net;
using Test1.com.netsuite.webservices;
using System.Xml.Serialization;
using System.Xml;
using System.Collections;

namespace Test1
{
    class Program
    {
        static void Main(string[] args)
        {
            NetSuiteService service = new NetSuiteService();

            service.CookieContainer = new CookieContainer(2);

            Passport passport = new Passport();
            passport.account = "xxxxxx";
            passport.email = "xxx.xxxx@xxxx.com";
            RecordRef role = new RecordRef();
            role.internalId = "3";
            passport.role = role;
            passport.password = "xxxxxxxxxx";