There are two main groups: the cursed, which include demons, zombies, bone dragons and werewolves, and the Imperial Guard, which is almost entirely comprised of human beings, but which has more advanced and lethal technology to rely on.
The battles in The Cursed are usually pretty fast, no longer than twenty minutes, with a relatively simple progression. First, you will have to create an operating base for your units, as well as collect the only resources available (energy and metal). You can use these resources to create new buildings and units.
The Cursed is a real-time strategy game that is geared towards combat. Control is pushed to the background to put emphasis on the battles between space marines and supernatural creatures.
There are additional maps on the official website.