Just read how this works and tried it. A bit tricky at first but actually quite easy once you get the hang of it. And it's kind of a fun exercise. Now I'm wondering if I should get a Didgeridoo too.
50mm/2” PVC pipe with a bit of beeswax on the end to protect your lips is a quick way to test out whether you want to spend the time to track down a proper didgeridoo.
circular breathing is useful for other instruments as well, though it's not typically a technique that's necessary until you get to fairly high levels.