Hi
PIN: A user-entered numeric key protector that can only be used in addition to the TPM.
Enhanced PIN: A user-entered alphanumeric key protector that can only be used in addition to the TPM.
Recovery password: A 48-digit number used to unlock a volume when it is in recovery mode. Numbers can often be typed on a regular keyboard, if the numbers on the normal keyboard are not responding you can always use the function keys (F1-F10) to input the numbers.
Recovery key: An encryption key stored on removable media that can be used for recovering data encrypted on a BitLocker volume.
More detail see BitLocker key protectors and BitLocker authentication methods.
Configure use of passwords for operating system drives:
This policy controls how non-TPM based systems utilize the password protector. Used in conjunction with the Password must meet complexity requirements policy, this policy allows administrators to require password length and complexity for using the password protector. By default, passwords must be eight characters in length. Complexity configuration options determine how important domain connectivity is for the client. For the strongest password security, administrators should choose Require password complexity because it requires domain connectivity, and it requires that the BitLocker password meets the same password complexity requirements as domain sign-in passwords.
More on: Configure use of passwords for operating system drives
Configure minimum PIN length for startup:
This policy setting is used to set a minimum PIN length when you use an unlock method that includes a PIN.
More on: Configure minimum PIN length for startup
Also more questions about BitLocker Key Management FAQ and BitLocker Group Policy settings.
I hope this information above can help you.