How do I retrieve my keychain password?

My MacBook forced me to make a OS update, so it shut down and restarted. After the new installation had been made, it asked me to log in. I thought it needed my Apple ID and password, but it was the OS log in and password. I did not know the password so then it asked if I wanted to creat a password keychain.

Any help how I can retrieve the OS password or keychain password?

I just keep getting dialogue boxes that I am blocked from because I don't know the password.