Not a problem. We all had this sort of question when we started.
It's really going to depend on where you put the broadcom-wl-22.214.171.124.tar.bz2 file that you downloaded.
Lets say for the moment that I put it into my "Download" directory. Before I could extract the parts from the file with the "tar" command, my command prompt would need to be showing that it was located in the Download directory. I expect that if you look at yours after using the "su -" command it is showing something like:
the ~ tells you that you are in roots home directory.
on this machine I would then use the command:
to change directory (cd) to the place where the broadcom file is.
issued then will show you the contents of the directory you are in and it should show the file you downloaded.
The cd command above starts from the top of the file tree and is needed because you are not in an adjoining directory to where you want to be.
When you want to move into the 'driver' directory I mention, you can then use
no forward slash or full path needed because the 'broadcom-wl-126.96.36.199' directory is off the directory you are already in.
You should then be able to use the b43-fwcutter command I list next.
Hope that helps, come back with any questions.
By the way, unlike DOS, directory names and File names in Linux are case sensitive, that's why I used a capital 'D' for Documents. It won't work if you omit it.