Read man pages. The first UNIX like system I used was a VAX-VMS
Er, VAX-VMS was not remotely UNIX-like and did not have a "man"
command, nor "ls", "cd" or any of those.
The directory-listing command was not "ls", it was DIR or indeed any
abbreviation of DIRECTORY. To change directory, instead of "cd", you
used SET DEF. The help command was HELP, not the obscure "man". And so
VAXen ran Unix - indeed, Unix was developed on VAXen. But the native
VAX OS, although much much later rated POSIX-compatible, was VMS which
is nothing like Unix in any way.
Indeed back in the day I used VAXstations with VMS and DECwindows -
there's one downstairs, waiting for a new hard disk, in fact - and I
don't think they even had an "xman" command.
Were you perhaps thinking of Ultrix or something?
Your general point - that reading man pages is a good way to learn - I
entirely agree with, but your example is incorrect.