mkdir is the linux command used to create directories. You will hear directories referred to as folders.
The above command line would be used to create a directory named knoppixtest.
mkdir -p knoppixtest/3.9
The mkdir has a useful argument other than the directory name. The parent directory option is very nice. You can create a directory and all of the parent directories above the last directory in the directory path list that is separated by the slash, /.
mkdir knoppixtest mkdir knoppixtest/3.9
For example these two commands are the same as issuing mkdir -p knoppixtext/3.9.
mkdir -p /var/spool/mail
As the number of directories increases, then the create parent option becomes more valuable.
Compare the above command sequence with
mkdir -p /var/spool/mail cd /var/spool/mail
The parent option can save some time.