The UNIX file system allows for the creation of subdirectories to
help organize files according to purpose or similar function. To create a
subdirectory, use the mkdir command:
mkdir <directoryname>
Issued without a path, mkdir creates a subdirectory
of the current working directory. The command mkdir can
be used to make a subdirectory anywhere in the directory tree
by specifying a path before the directory name:
mkdir 
/smalltalk/source/<directoryname>
Giving the mkdir command in this way assumes that you have
already created the parent directories specified in the path. mkdir
will return an error if any of the parent directories do not
exist. If you wish mkdir to create all the directories
in the tree that you specified, use the -p option.