Jim wants to use an app called Morpheus, but it can't be installed through the Google Play Store. He's been told he needs to be in Developer Mode to install an app from somewhere else. Leo says that's a bad idea because it'll make his Chromebook less secure. Not all apps are approved for ChromeOS. If he can't install it and run it directly from the Google Play store, he shouldn't do it.
Morpheus is a piracy app, which explains why it's not installable. But if he is committed to doing it, he can turn on Developer Mode. The good news is that if he does get bit, he can always Powerwash the Chromebook and get it back to its secure configuration.