How-To Enable your Hook
To enable hook
Open your developer console by pressing the "~" key. If you are unable to get to your developer console, follow the instructions here to enable it.
Type this in console.
bind x +hook <-- Replace the "x" with what ever key you wish.
Press enter key
Resume game.
Now where ever you point your weapon and press and hold the key you chose above, you will be dragged to that location.
While you are being dragged through the air, you can re-point your weapon, and release and re-press the key you just bound, to achieve the flying effect you see so many people use on the server.