Create a new trigger. Go to Edit -> Convert to Custom Text.
You will see that there is a script now. Hit Ctrl + A to select all of the text and then delete. Go to the Jass script that you need, Ctrl + A again to select the whole script and while selected right click and hit "Copy". Go to the space that you previously deleted and right click "Paste" or Ctrl + V.
There is a possibility that the system you are trying to implement requires variables or other scripts. If it requires variables, there will be directions in the green part of the text, telling you exactly which variables to create and of what type.