Your SQL Server product key is entered during setup, or can be added afterward if you installed using a trial or evaluation edition. Here's how to do it after receiving your key.
During a fresh installation
In SQL Server Setup, on the Product Key step, select Enter the product key.
Type your 25-character key exactly as provided and continue the installation.
On an existing installation
Open SQL Server Installation Center from the Start menu.
Go to Maintenance → Edition Upgrade.
Follow the wizard and enter your product key when prompted to convert the evaluation/trial instance to a licensed edition.
Confirm activation
Run SELECT SERVERPROPERTY('LicenseType'), SERVERPROPERTY('Edition'); in SQL Server Management Studio to confirm the instance is running under your licensed edition.
