When you open a new Unix shell, you start in some directory, probably your
home (~/) directory. If you use pushd to navigate to different
directories, there is a paper trail of your movements, a listing of where
you've been. You can view this listing of directories with the dirs
command.
$ dirs
~/
$ pushd code
$ dirs
~/code ~/
$ pushd /usr/bin
$ dirs
/usr/bin ~/code ~/
Each time you pushd, the directory you have moved to is pushed onto the stack of
visited directories. Alternatively, you can use the popd command to return
to the previous directory, removing the current directory from the stack.