You've got a stock Pi up and running and are vaguely familiar with the command line
sudo nano /etc/hostname
This will open an editor to let you change the hostname of your pi. Change it to something memorable like your full name or your dogs name, then press Ctrl+X then Y to save it. Then reboot your Pi
Get yourself to a source directory to play in:
cd
mkdir src
cd src
Download the WebIDE installation files from Adafruit:
curl "https://raw.github.com/adafruit/Adafruit-WebIDE/alpha/scripts/install.sh" | sudo sh
Start the WebIDE service on port 80 by default
sudo service adafruit-webide.sh start
On your pi or another computer open your web browser to http:// and Adafruit will walk you through the set-up.
Beyond this point it's so well documented it's not worth talking about.