Coming in at around 12GB on the PC, the Halo Wars 2 beta is now live. You can download it for either the PC or Xbox One.

The beta focuses on the Blitz game type and fortunately for you, the Halo Waypoint has a good overview and primer on what Blitz is all about.
Blitz is a new addition to the Halo Wars experience offering a twist on RTS gameplay that combines the deck building and split-second decision making of card-based strategy play with explosive tactical combat in the Halo universe. Your card deck, along with your faction leader, are your greatest resources as you assemble a collection of air, ground and infantry units and seek to out-think and out-maneuver your opponents on the battlefield. Blitz is a PVP gametype that offers 1v1, 2v2 and 3v3 configurations via Xbox Live matchmaking.

There is a lot more on Halo Waypoint, so be sure to read up on Blitz.