More clarification on createdb command

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/11/tutorial-createdb.html
Description:

When I first followed the command, I first couldn't understand which shell
to execute this in - the psql shell or the normal command line. Although a
small point, specifying this could make life easier. :)

Another thing I noticed is that when I followed this on my Windows 10, it
asks for a password. My laptop is just a stand-alone, and isn't connected to
any LAN. During the installation, the only password it asks for the postgres
superuser. When I try entering that password, I get an error - 
createdb: could not connect to database template1: FATAL:  password
authentication failed for user "HP", 
where the name of my laptop is HP.
To rectify this issue, I had to make a new user in the pgAdmin (at least, I
initially used pgAdmin, but later realized that it could be done using SQL
itself on the command prompt). I don't know any workaround for this issue,
but maybe specifying that could be more helpful for beginners like me ;)