The generator gamemode is a gamemode where players can buy generators, that generate sellable items. Using the money they got from selling they can upgrade the generators to get items that sell for more, or buy new generators.
You also got sellwands, which are special items that if you right click on a chest with them will sell its contents instantly. Sellwands also have multipliers, so you can have an x2 sellwand which doubles the received money from selling.
Players also have generator limits, which means they need better ranks to get the ability to place more generators.
That's basically it. This plugin doesn't (YET) implement a shop, but you can easily combine it with a shop plugin and sell generators and sellwands, as they are just items.