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.
Quite right, none of this Unix nonsense... we used to have VML and God
knows what else... oh, I guess we'd better mention "edt" or (if you
were really advanced and modern) "tpu"... if you couldn't do it with
the numeric keypad on a vt200 terminal then it wasn't worth doing...