Browse to https://script.google.com/ Start a script and paste in the delete.gs code.
After you paste it in, save it. In the drop down at the top select the function you want to run. For example, you could run the batchDeleteEmail function.
Next click the little clock looking button. This is for your triggers. You can set up how frequently you want the script to run (I did mine for every minute but others are seeing execution take longer than a minute in which case you may want to run every 5 or 15 minutes).
Also, you can change the code given in delete.gs according to your own circumstances.