The developer’s own Gameplay description sums it up quite well:
Build your junk ships to literally any shapes and sizes and fight against the creations of other players in 7v7 PvP capture arenas across 3 new maps. The more you fight the better ships you can build. Pick one of the classes (Frigate, Cruiser, Battleship and Destroyer) and research all the blocks to build your ultimate junk ship. Every classs has its own role in the team.
Those new maps refer to the ones added with the release-day patch, which also includes a new game mode, a new chat interface, and a class system overhaul. Then, of course, you have your usual bevy of balance changes and tweaks.
But you can more over here.