You'll first want to setup your Raspberry Pi with an operating system on an SD card. You can learn how to setup an SD card for you Raspberry Pi, if you haven't already done that. We also have an entire series on how to get started with your Raspberry Pi that you may find useful if you're new to the the world of Linux and Raspberry Pi.
The next step to continue on with the tutorial will be to install the WebIDE. We have instructions for installing the WebIDE as well. It's a fairly straightforward, and quick process to get the WebIDE installed.
Once you have both of those components setup, and installed, test that your WebIDE works by going to http://raspberrypi.local on any computer on your local network.