Go to Server Manager
Add roles and features -> Role-based feature-based installation -> Features -> BitLocker Drive Encryption
Do a full restart
Then, Open Local Group Policy (gpedit.msc)
Do another full restart
Go to Control Panel
Open System and Security -> BitLocker Drive Encryption
Enter your password and then save it to file, afterwards you must do the last restart and check if server asks you enter password to unlock the drive.