How to use the opensea-js.OpenSeaPort function in opensea-js

const opensea = require('opensea-js')
const OpenSeaPort = opensea.OpenSeaPort;
const Network = opensea.Network;
const MnemonicWalletSubprovider = require('@0x/subproviders').MnemonicWalletSubprovider
const RPCSubprovider = require('web3-provider-engine/subproviders/rpc')
const Web3ProviderEngine = require('web3-provider-engine')

const MNEMONIC = process.env.MNEMONIC
const INFURA_KEY = process.env.INFURA_KEY
const FACTORY_CONTRACT_ADDRESS = process.env.FACTORY_CONTRACT_ADDRESS
const NFT_CONTRACT_ADDRESS = process.env.NFT_CONTRACT_ADDRESS
const OWNER_ADDRESS = process.env.OWNER_ADDRESS
const NETWORK = process.env.NETWORK
const API_KEY = process.env.API_KEY || "" // API key is optional but useful if you're doing a high volume of requests.

if (!MNEMONIC || !INFURA_KEY || !NETWORK || !OWNER_ADDRESS) {
    console.error("Please set a mnemonic, infura key, owner, network, API key, nft contract, and factory contract address.")
    return