$HOME
From Hackepedia
Many examples will use $HOME, so this page is here to let you know that on UBOs, $HOME is your home directory. If my username was frank, I could do:
$ grep frank /etc/passwd | awk -F: '{print $6}' /home/frank
I can see my home directory is frank. If I want to go there I can type
$ cd /home/frank
to change directory there. There are also a few shortcuts to get to your $HOME directory.
$ cd $HOME
and even easier
$ ~
will put you there.
pwd
(print working directory) will show you which directory you're currently in.