Roblox is a sandbox game sort of like Minecraft, but with way more power given to third-party developers and users to develop and distribute content in it. What you'd consider mods for other games are the whole point of Roblox, and MTX can be implemented by those third-party developers using "Robux" as a currency. The MTX can be your usual MTX fare of skins and power-ups, but also often abused for less ethical purposes, like gambling mechanics. The fact that Robux can be cashed out for real money via official and unofficial methods mean that's it's ripe for abuse.

Update: Also, I wasn't aware of this before the article, but apparently gambling sites have figured out a method to link a Roblox account to their external sites, and then use the user's Robux wallet as currency in their illegal online casinos.

The way I understand it, it's basically a game engine that kids can use. I don't think Roblox itself is actually a game; you use it to make games.

Don't know what the microtransactions are for, however.

Roblox is a platform where some users create games and other players play them. It's grown to be a pretty powerful platform/engine, but is now significantly more complex than it used to.

Roblox has the ability for users to add micro-transactions to their game. Essentially, users get a small portion of the micro-transactions back as real-world currency. It's up to users/developers who make those games to choose what players get in exchange for these micro-transactions.

As far as I can tell, the quality of games has dramatically increased since I quit. My guess would be that the users/developers making games are now adults, and the players are still kids.

A galaxy brain way to use children as labor to make shitty games. And the kids even have fun doing it.