Basically, you’ll drop into a map with 39 other players, fight for survival, fight the wilderness, fight for each other. You know, just lots of fighting. Fight fight fight fight fight. Currently, there are roughly 12 heroes available. There are 9 others, but they must be earned through in-game means, specifically, you have to rent them 50 times first. Or, you know, you could just drop some cash on them instead.
Check out the patch notes for the full list of what to expect.