If you are not familiar with Linux and the Raspberry Pi, see the following websites for more detailed instructions and help:
To set up a Raspberry Pi as border router, you need the following hardware:
It is sufficient to set up the Raspberry Pi in headless mode, thus using remote access instead of a screen and keyboard. However, if you prefer to set up the Raspberry Pi with screen and keyboard, you additionally need the following hardware:
First, you must install your Raspberry Pi with an operating system image. To do this, you download the image to your computer and write it to the SD card, which serves as "hard disk" for the Raspberry Pi later.
On your computer, download the Debian Wheezy version of the latest Raspbian OS image from http://www.raspberrypi.org/downloads/.
Unzip the image file and write it to the SD card. See http://www.raspberrypi.org/documentation/installation/installing-images/README.md for instructions on how to write the image to the SD card. Instructions are provided for different operating systems. Make sure to follow the instructions closely, because small errors (like selecting a wrong device) might destroy the data on your computer.
After writing the image, remove the SD card from you computer and insert it into the Raspberry Pi. Connect the ethernet cable and power supply (and screen and keyboard, if desired) and power up the Raspberry Pi.