Question about robux

I’ve never understood how this works.

Say premium payouts or whatever the thing they’re doing now, does Roblox give players the money by generating it out of thin air, literally just changing their amount of robux from 0 to say 10 robux? Or do they actually somehow pay for that Robux to then be given? Because it is virtual currency, it must have value, right?

Or say a player purchases an item, a commission goes to Roblox. I never understands this, why would they do this? They’re taking Robux so they can - pay themselves? How do they transfer it, do they even collect the money or is it just a way to control the market or something.