I frequently use Variant IDs in solutions that I make for my customer's Shopify stores. But oddly, the Shopify Admin UI does not show Variant IDs. So here's how to find the Variant ID if you need them for your store.
Go to your product in your Shopify admin. Add .xml to the end of the URL where the arrow is pointing to.
This will give this XML view of the product information. The location of the Variant ID is highlighted.
I hope that helps.