Normaly, to slide you need first to start running. After the end of total acceleration you will be able to slide.
You can use multiple directions and target your aim to different directions while simultaneously slide to different directions.
To perform a 360 sliding you need to push "Shift" to run and then "C" and give the direction of sliding with "W" "S" "A" "D". For example, you push "Shift" to run and "W" + "D" and look at 45 degrees left: You will slide 45 Degrees right but you aim will focused left cause WASD is giving the direction of the movement and not the mouse!
Sooo... To make a 360 you need to push "Shift" to run, press "C" to slide and hold "W" and turn your mouse a 360 circle! You also can change the direction of the initial sliding direction!
Hope you will enjoy it!