The mkdir 7 in command

what is it asking for number 7

Exercise: 7. mkdir

Is this the task that you are having doubts about:

Navigate to the 2014/dec/ directory.

yes it is the right one

The change directory command works like this:

cd <destination>

Depending on where the 2014/dec/ directory is compared to where you are now, you may be able to:

cd 2014/dec/

If that doesn’t work, post a screenshot so that we can see what you see.