Please help me come up with a new method to install AUX

[LewisMT]

Hi I've just bought my GTI and have been looking into the best way to install an aux input for the stereo. I've had a look and found this method
Could someone please come up with a tutorial on how to install this, it looks like you just plug it in and that's it but I don't want to break anything or mess it up.

Thanks