This is actually fun and one of the rare free to play indie game that isnt a complete scam, you get attack cards which you have to do a motion with your mouse to perform and then you defend the attacks of your opponent (with a motion of your mouse to defend and if done properly a motion to counter the attack with a counterattack). You can unlock every fighting styles (which change the stats you get in battle), you can also start a fight with your friends or complete strangers.
Dont try it on cellphone, its complete trash there, way better on a tablet or just your average computer.