You need to start your programs up in the correct order so that they will work properly.

  1. Start McMyAdmin and your CraftBukkit server
  2. Start a Minecraft game linked to your local McMyAdmin server
  3. Open up Scratch, and enable the experimental plugin
  4. Launch IDLE, and from the File menu select ‘Open’.
  5. Navigate to the mcpi-scratch.py file in your mcpi-scratch folder.
  6. Select ‘Run Module’ from the Run menu in IDLE. A new window will open displaying the output of the Python program running. It is safe to minimise it and carry on.

You should now position your Scratch and Minecraft windows side-by-side to view everything that’s happening.

https://youtu.be/wWIG-Cq4eLg