Firefox Plugin trouble

I have now gotten the plugins sitting on my desktop, ready to install. I'm pretty sure I have to run something through the terminal to install them, but every time I try I can never use it right. I follow the post in the ubuntu forums I read (here) about the basics of using the terminal but I still cannot even change directories. I'm an old DOS head and I feel so dumb. Is it the exact syntax I'm not getting right? I know I have to put the filename in right but I DO. I suppose I can do nothing but keep trying, of course I will post what I find.