Find a PC
First things first, you need to find a machine. You could of course check out your local tip, but other good places to look are Freecycle, Snaffleup or Gumtree – all of which are likely to have free offerings and they're likely to be in better shape than the ones at the dump!
You'll also need an Operating System (OS). If you're lucky, the PC you've found will have a recent OS already installed. However, if the hard drive has been wiped or the OS is out of date, don't panic! There's no need to spend hundreds of pounds on Microsoft Windows.
Instead, there are free alternatives. For example, the open sourced, linux based operating system Ubuntu comes highly recommended. It contains all the applications that come with Windows and is free to install.
It also comes with the Mozilla Firefox web browser which is a faster and more reliable alternative to Internet Explorer.
If you're not using Ubuntu, you can download Mozilla's web browser Firefox for free, here.