In short, everyone who submit something an actual game receive 1 course on gamedev.tv of their choice for free.
There's no prize for the top or something, except the satisfaction of having made something popular.
Being part of the group (or having made something yourself) that made it to the top of this kind of open contest is also a great piece to add to a CV/Portfolio if you wish to land a job in the video game industry.
For a while now, every year GameDev.tv has launched this DevJam/GameJam for a free course for all participants who submit an actual game.
They have many great courses for Unreal, Unity and even Godot for various things. Be it for learning how to use an engine or up to the advanced stuff like Multiplayer as well as gameplay-based courses (like how to make a RPG, a RTS, a FPS, etc.)