Here is a link to some decently put together Audacity tutorials.
There is also a quick start guide that's only two pages long., and a step by step 6-page guide that takes you from recording to editing, then converting and exporting.
If you use the computer lab, you can borrow headphones with microphones and the students can create them in class. Once you have the students create the podcasts, they will have to save them to one spot. You might want to create a folder on student share or have them upload to VRspot.