Nafk is basically a more advanced version of splix.io. You have the option to choose a custom flag which will represent your territory and have the ability to use special abilities that will help you in both attacking and defending.
In the world of Nafk.io you play as a long worm, initially you start off in a very small area owned by yourself, to expand this and claim more for yourself simply move through the flag and draw the border you want to expand to with your body. You can do this as many times as you want and make a huge flag, as previously mentioned you also have special abilities to use. You have 3 at your disposal so far, a speed up, a camouflage and a zoom out. Although the last one doesn't seem like too much of a 'special' ability its one of the most useful!
You move your worms body through use of the arrow keys and use your abilities using Q, W and E, the corresponding ability will be shown in a little image on your screen so don't worry about getting confused or forgetting.