Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
For a Microsoft 365 subscription bought from a retailer like Best Buy, the subscription effectively begins when the product key is redeemed/activated, not at the time of purchase.
After buying, the product key must be entered (for example via setup.office.com or using the Enter Key option in an Office app). The subscription does not actually start until that key is redeemed.
References: