Su command issues

I’m new to linux and parrot but I’ll get there. I’m working
through a book called “The Linux Command Line” by
William E. Shotts, Jr and going throughthe section on su
and sudo I tried typing su --login and when asked for a password I gave mine. There are no other users on this
computer and I am the superuser. To act as root I type
sudo su and enter my password and become root. I did the installation so I know there are no other passwoords but when su --login asks for a password mine is refused.
How can this be? If anyone can tell me what’s going on, I’d appreciate it. Thanks

Maybe learn from this is easier?