The purpose of BitLocker is to encrypt the full volume to protect your data from unauthorized access.
Not only on Windows 10 and Windows 11, BitLocker is also available on even earlier versions of Windows. BitLocker is included with Microsoft Windows versions starting with Windows Vista. But it is available to all editions of Windows such as the Home edition of Windows 11/10/8.
BitLocker is a full-volume encryption method, designed to protect data by providing encryption for entire volumes. It can encrypt the operating system drive via the hardware level(TPM) or the software level(a password or a startup key on a USB flash drive). Besides, it enables you to encrypt external storage media with BitLocker.
During the setup process, it automatically generates a Bitlocker recovery key and asks you to save it in a way. The BitLocker recovery key is very important and you should keep it well. Only if you have the password or the BitLocker recovery key, you can decrypt the drive to make the data readable.
When your computer which contains your BitLocker encrypted drive is lost or stolen, or the BitLocker drive is disassembled and inserted on another computer, it requires the password or the BitLocker recovery key to access the data. So if you have important or private files on your computer, you can enable BitLocker to prevent data leakage.