A regular Linux and Unix user should know how to use the PATH, CDPATH, MANPATH and HOME environment variables, in the bash shell.
Display the PATH and CDPATH with echo, like any other variable:
$ echo $PATH
$ echo $CDPATH
The MANPATH is used by the Linux and Unix manual (man).
Display the MANPATH:
$ manpath -g
The HOME is not PATH-like, but it is often used in shell scripts, and it is the same as tilde ~, expanding in the user’s homedir.
$ echo $HOME
You can see a list of the most common PATH-like variables here.