Global settings allow you to configure how Inventory and stock is managed in your WordPress install, and also a number of thresholds that can apply to all products in your shop.
Go to WooCommerce → Settings
Click the products and then the title inventory link
Check the Manage Stock option to enable stock on all products. If you have a mix of virtual and physical products, you can skip this option here and enable stock on individual product posts (explained in the next section)
This step is required before updating stock levels from Selro.