Fullscreen is finally investing in their verticals, so when a channel is accepted into Fullscreen, it's placed in one of those verticals, which are represented by its hub channels. So if you're a gaming channel, you would get placed in Fullscreen Arcade. A beauty channel would be placed in Beautique and so on. The reason they do this is for advertisers, so a company that is looking to advertise can target a particular genre like gaming. It means more money for both you and Fullscreen.
Fullscreen Go is a network where you have access to the same tools and promotions of Fullscreen partners while you grow your channel to a point where one of the hubs takes you. The only real differences are a standard contract and you won't have access to the hub for hub promotions/uploads.