If you have a 25-character product key, you can activate it through several official methods: :

This is the fastest method if you have a working internet connection.

If your computer is offline or the online activation fails, you can activate via telephone.

Product keys, also known as activation keys, serve as a unique identifier that verifies the authenticity of a software product. In the case of Windows 7, the product key is a 25-character code that is used to activate the operating system, ensuring that it is genuine and has not been tampered with. The primary purpose of product keys is to prevent software piracy and ensure that users adhere to the licensing agreements.

If Windows is already installed but not activated, type wmic path softwarelicensingservice get OA3xOriginalProductKey into an Administrative Command Prompt to retrieve it from the BIOS. Method 1: Online Activation (Primary)

Look for a Certificate of Authenticity (COA) sticker on the side or back of your desktop, or the bottom of your laptop.