Please, play nicely. We guys here should help other rather than dumb each other. We are a very colorful and different community, so people might not get each others humor, which is kinda hard via text anyway, so just be friendly to each other and don't take everything too harsh. Talking to you BOTH!
A google-search will not always help people. So just tell them what you know / have found and WHERE you get it from. This is a forum for everyone, newbies and advanced users, so keep that in mind and be respectful.
Alright, I also merged your posts Blue2ewth, as double-posting is not allowed in here.
I advice you both to re-read the RULES
of this forum and follow them accordingly.
So to your problem:
As the "/usr/share/themes/" folder is outside your home-directory, you have to be root to copy to it. Also, if you are copying a folder, you have to use the "-r" flag for "recursive". The command(s) for you would be:
cp -r ~/Desktop/PlasmaFire /usr/share/themes/
sudo cp -r ~/Desktop/PlasmaFire /usr/share/themes/
It's also possible to create a ".themes" folder in your home-directory, and copy the folder to it, but I like to use the global one, as I can also theme the root-applications then.
BTW, same goes for the folder "/usr/share/icons/"
Have a Nice day! Cheers~