Apps :: How do I install stuff?

I hope someone can help me. I accidently asked this question in another section. I have installed DSL.DK (a danish version) to my harddrive beacuse mandrake was far to slow. I tought it had all I needed and it allmost does except Flash support in the browser. So I need to install this somehow. I tried following a debian tutorial on the apt package thingy (I havent used a package system before) but I ran into problems when I tried the following command from root

apt-setup

It didn't recognize this command. So now I dont know what to do. I thought I could just download the newest version of firefox and I have downloaded the file ok but I dont know what to with it?? Please help!

original here.