BitLocker To Go is BitLocker Drive Encryption on removable data drives. This includes the encryption of USB flash drives, SD cards, external hard disk drives, and other drives formatted by using the NTFS, FAT16, FAT32, or exFAT file systems.As with BitLocker, drives that are encrypted using BitLocker To Go can be opened with a password or smart card on another computer by using BitLocker Drive Encryption in Control Panel.
BitLockerAutoUnlock can be configured to automatically unlock volumes that do not host an operating system. After a user unlocks the operating system volume, BitLocker uses encrypted information stored in the registry and volume metadata to unlock any data volumes that use automatic unlocking.
Source : https://docs.microsoft.com/en-us/windows/security/information-protection/bitlocker/bitlocker-overview