This question is so basic it shouldn't be asked. Please read a book like
http://linuxcommand.org. Not necessarily all its 700 pages, but do read the first few chapters.
The command to remove a directory is
rmdir. However, if the directory contains any files, it can only be removed after removing those files. You can remove a directory and the whole directory hierarchy below it with
rm -r, but this is a dangerous command, as you can remove the wrong files if you make a small typing mistake.
