What is Google Shopping?
Google Shopping provides sellers access to millions of shoppers on the Google platform. Shoppers can search for products on Google's product tab.
You or digital marketing agencies can also use this feed to create product based ad campaigns.
Accessing the Feed 
To access your feed, go to your eCommerce site and add /product-feed.txt to the end of your domain name in the browser. It will look like this:
[yourdomainname.com]/product-feed.txt
Data from your product inventory list is pulled directly into the feed and updated every 24 hours including stock levels.
Merchant Centre Setup
To showcase your products on Google, you'll need a Merchant Centre account. Follow Google's tip on setting up your account. You'll need access to your domain registrar to verify that you own the account.
From the Your Business section, ensure all information under Shipping and returns and Business info is completed, or products may not be displayed on Google.
To add the feed, go to Product, the Add Products button then select to add from a source. Select Add products from a file and enter the feed link. Google will not publish products instantly as they need to be verified. This may take 24 to 72 hours. Any products not approved can be reviewed individually and updated accordingly. Product policy violations will be listed if a product is not approved.
Google Feed Optimisation
You may wish to update your product data from the back office to optimise your feed. Here's some recommendations:
Product title
Include top keywords and order them by importance left to right
Use the most commonly used name for the product
Include brand, gender, product type, or even model number and occasion
Do not use ALL CAPS or promotional text such as "On sale now"
Do not keyword stuff or exceed Google's 150 character limit
For example:
Brand + Product Type + Gender + Keyword 1 + Keyword 2 + Colour + Size.
The colour and size will be automatically appended for variant products.
Product description
Include the most important information in the first 180 character including the brand, who it's for, the product type, material, pattern, texture, intended age range, size availability and special features where relevant
Do not use ALL CAPS or promotional text such as "On sale now" or "Free shipping"
Do not include a description of the brand (you can use the "additional information" field if you wish to include brand information on the product page)
Do not include descriptions of other products, compare with other product or include links to other websites and internal linking (at least not in the first 180 characters)
Do not include billing or payment information
Brand
Brand is very important to how Google indexes your product listings and displays products in relevant search results. Ensure it's complete!
Model number (a.k.a MPN)
False or incorrect data will prevent Google from matching your products. This is the information provided by the supplier and is generally what suppliers use to fulfil purchase order. If you do not have the information, leave the field blank. You can use SKU instead as an internal identifier.
GTIN/UPC/EAN
False or incorrect data will prevent Google from matching your products. This is not a Saledock generated barcode. This is the barcode provided by the supplier. If you do not have the information, leave the field(s) blank. You will generally only have 1 of the 3 options for each product.
Leverage Google's Product Taxonomy
To enable Google to better understand what you are selling, Google requires you to assign categories from their product taxonomy list. This is not mandatory but it is highly recommended.
To assign a category, view the eCommerce tab on the product details page, and scroll to the Google Taxonomy and Metadata section:
For Apparel products, we recommend supplying the Gender and Age Group of the item.
Colour
Write out the full colour, for example Green instead of G. Ensure the colour is an accurate representation of the product colour.
Size
Keep your sizing consistent, for example S, M, L. Don't use a mixture such as S, M but then use Large written as the full word.
Images
High-resolution images at least 800px x 800px
The first image to be of the product on a white background taking up between 75% - 90% of the full image
Consider close-up secondary product images to showcase your product and lifestyle images of the product in action/being used
Don't use logos, generic images, promotional text or call to actions in your images