WikiLeaks
Tor
Tor is an encrypted anonymising network that makes it harder to intercept internet communications, or see where communications are coming from or going to.
In order to use the WikiLeaks public submission system as detailed above you can download the Tor Browser Bundle, which is a Firefox-like browser available for Windows, Mac OS X and GNU/Linux and pre-configured to connect using the anonymising system Tor.
Tails
If you are at high risk and you have the capacity to do so, you can also access the submission system through a secure operating system called Tails. Tails is an operating system launched from a USB stick or a DVD that aim to leaves no traces when the computer is shut down after use and automatically routes your internet traffic through Tor. Tails will require you to have either a USB stick or a DVD at least 4GB big and a laptop or desktop computer.