To find an ID for something in your Shopify account, start by opening your Shopify admin area. Then, navigate to the specific resource whose ID you're interested in. Lastly, look at in your browser's address bar: the ID is the number at the very end.
This applies for every kind of resource that you'd configure with an ID, whether it's an order, or a location, or a variant. For example, if you're looking at an order, the URL will look something like this:
And in this example, the ID is still the number at the very end.
If you're not sure how to find the ID for the resource you need, click that chat button in the corner. :)