The mkdir command makes a directory on a UNIX system. To make a directory, change to the directory under which you want the new directory to live. Then, type mkdir directory, where directory is the name you want to call the new directory, and press <Enter>. If you have permission to write in the current directory, and there is no directory already named directory in the current directory, the new directory is created.
The rules on naming directories are the same as the rules on naming files: do not use a name longer than 256 characters, and do not use the filename metacharacters , ?, [ ... ]; otherwise, anything goes. A useful convention is to always start directory names with a capital letter. This way, you can differentiate between a file and a directory without doing a long listing (l).
You can make several directories at once by typing:
mkdir directory1 directory2 directory3
Try creating a directory for memos and a directory for reports:
mkdir Memos Reports$