To play Knife.io, use your mouse to control your character’s movement, navigating the arena to avoid enemy knives. Click the left mouse button to throw your knife at opponents, aiming carefully to hit them while dodging their attacks. Collect power-ups or orbs that may appear to gain advantages, such as extra lives or enhanced abilities. Survive as long as possible by outsmarting and outmaneuvering other players. Defeating opponents may reward you with extra lives, helping you stay in the game longer. Practice your timing and aim to become the ultimate knife-throwing champion.