If you are using IntelliJ (which is the IDE Treehouse recommends) then you should have a "Gradle" tab that you can click on over on the right sidebar of the IDE window. If you can't see that button then you can open the window by clicking on the "View" menu on the top toolbar then "Tool Windows" then "Gradle".

Once the Gradle window opens up you just need to expand the "Tasks" and "treehouse" options and then double click on the "prepareSubmission" task.

Thanks andren and Craig Dennis - I didn't have the gradle plugin installed; once I got that, I was able to follow along. I'm liking the course so far.