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What exaclty is this and can i turn it on or is it already on?
This is Likwid
It's already on. It jus means that when your aim cursor is around the enemy, its like a magnet. It helps, but that doesn't mean its easy.
More specifically your look sensitivity drops way down when your crosshair is near an enemy so you can aim more precisely. Friendly targets like teammates don't give aim assist. For comparison try killing a teammate with a BR and see how hard it is to aim without the assistance. The truth is the controller is an extremely clumsy and imprecise input device for a shooter and the aim assist plays a huge part in everyones score at the end of a game.