To find a product ID, go to the Products > All Products window and hover over the product name. The ID will be shown at the start of the line that appears.
You can also see it in the URL when you have opened the product for editing.
To find the product category ID:
tag_ID=164where 164 is the ID of the category.
Order ID are shown in front of the name in the Orders window.
You can also see them in the URL and on the main page when you open an order.