Hi guys!
Just got a guitar, and I’m wondering how do I hook it up to the Cubase 5 Essential on my PC??
I have a extern soundcard; M-Audio, Fast track pro.
Do I need some kind of a special cable to do it?

Read the Getting Started manual and the manual for your soundcard and then come back and tell us where it went wrong. This is a really basic question so reading the manuals is the best way for you to learn seeing your lack of knowledge.