Bitwarden stores a password just as it does right now.
Let’s assume it’s 123456
Theres is also a password that’s the same for all entries in BitWarden.
Let’s assume it’s abcde
This password isn’t stored in the BitWarden database.
When BitWarden enters a password it enters 123456abcde.
The advantages.
A] If the database somehow gets compromised the attacker still doesn’t know the password because abcde isn’t anywhere is the database.
B] The database can be shared with anyone. In your last will you give abcde, so others can unlock the database.
The ‘abcde’ password is asked on same screen the master password is entered.