Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
If you purchased directly from Microsoft, you usually don't see a product key. The Office subscription will become associated with your Microsoft account at https://account.microsoft.com/services. Use the account to install Office on your PC. Use the account credentials to activate the product.
On the other hand, if you purchased from a third-party seller (not Microsoft), you should have been provided with a key. Follow the seller's instructions for the install.