How to create a product group using google ad words API in PHP

[ShareSoft Technology]

I am new to google ad words.

I need to create a new product group. I have used below library to do that process.

https://github.com/googleads/googleads-php-lib.

I tried add Shopping campaign to create a new product group.

https://github.com/googleads/googleads-php-lib/blob/master/examples/AdWords/v201806/ShoppingCampaigns/AddShoppingCampaign.php

I want to know if that method is correct or not. If the method is correct,

const BUDGET_ID = 'INSERT_BUDGET_ID_HERE';

const MERCHANT_ID = 'INSERT_MERCHANT_ID_HERE';

I want to know where can i get "BUDGET Id". Otherwise please provide the sample code to create product group using google ad words API.