Go to Privacy & security > Windows Security > Device security. For Windows 10, go to Update & Security > Windows Security > Device Security instead.
Click Manage BitLocker drive encryption under Data encryption.
If you can’t find this option, enter control /name Microsoft.BitLockerDriveEncryptionon Run(Win + R) to open the program.
Expand your drives by clicking on them.
Click on Turn on BitLocker for all drives you wish to encrypt.
For your OS drive, it will warn you that you won’t be able to use the Windows Recovery Environment after encrypting the drive. Click Next to process.
For other drives, check Use a password to unlock the drive and specify the passwords. If you wish to use a smart card, check that option instead. Click Next.
Choose how you want to back up your recovery key and follow the instructions. I recommend saving the key (or file) to a USB flash drive. You can also save it in multiple locations.
After that, click on Next.
Pick between the encryption used disk space or the entire drive and click Next.
Check the New encryption mode or Compatible mode depending on your need. Read the descriptions on the tab to learn their differences.
Click on Start Encrypting to begin the process.
Hit Close after the process completes.
Note: You can also right-click on the drives inside your File Explorer and select Turn on Bitlocker or Show more options > Turn on BitLocker to initiate the process.
Using Device Encryption
You can also use Device Encryption in some computers to encrypt your hard drives. It also uses the TPM like the BitLocker. But while BitLocker allows you to choose which drive to encrypt, this feature encrypts all connected drives.
Apart from the TPM, Device Encryption also has some more prerequisites:
Open Windows Settings by pressing the Windows key + I.
Go to Privacy & security > Device Encryption or Update & Security > Device Encryption.
Click on Turn on and wait until the process completes.
Note: If you can’t find the options, your system hasn’t met all the necessary requirements. Check System Summary > Device Encryption Support on System Information (msinfo32 on Run) to see why automatic device encryption failed.
Using Third-Party Software
You can also use other third-party encryption software to encrypt and protect your drives.
Most of these programs don’t use the TPM, so there’s no hardware limitation. Many open-source and free apps like VeraCrypt, AxCrypt, DiskCryptor, etc., are also available for this purpose.
If you want to encrypt your external hard drives, you may even find an OEM encryption application.