The author's avatar in "Murder Mystery 2," a popular Roblox game. Matt Weinberger/Business Insider If you're older than, say, 15, there's a healthy chance you've never heard of Roblox.

Although Roblox has been available for PCs since 2005, the game has exploded in popularity only over the last few years. The newer smartphone, tablet, and Xbox versions of the app have opened it up to a new generation of players, making it a smash hit on schoolyards and college campuses everywhere.

Nowadays, Roblox boasts 56 million monthly players. That actually puts it ahead of Minecraft. Earlier this year, Microsoft said about 55 million people play its hit game every month. Meanwhile, by some measurements, more people search for Roblox's website than for Lego, company officials boast.

Even more intriguingly, Roblox lets anybody build games using its technology — providing its mostly-teenage base of developers with an unprecedented entrepreneurial opportunity. Roblox recently announced that it's on track to pay out $30 million to developers this year, with the top earner set to rake in no less than $3 million.

In an effort to better understand the Roblox phenomenon, I asked the biggest fans I know. My nephews, 11-year-old Diego and 7-year-old Tony, have been teaching me the ins and outs of Roblox. Here's what I learned.