This is a pretty dumb question, but could someone please explain to me how to use the pitch correct/ pitch shift effect in Cubase Essential 5? 
What are you trying to pitch correct?
Vocals.
Page 22 of the included plugin reference manual gives a good description of the parameters.
Put it as an insert on the vocal channel that needs correction, and play with the parameters.
If you don’t know the scale, use chromatic and then use the correction tolerance and correction speed.
In other words, just play about with it until you work out how it handles.