Don't worry about it... I'm a newbie myself. Only been using Linux for a couple of months now.
If you want to change to a directory you have to use the cd command like in DOS (I think this is what you mean).
So, you'd type 'cd /home/David'
or you can always type 'cd ~' which will bring
you to your home directory.
Once you are there, type 'tar -zxvf blackbox-0.61.1.tar.gz' to unpack the archive. You shouldn't type unzip in there anywhere.