It is actually quite simple babes
http://www.quidco.com/terms-and-conditions/
Join quidco and they have a list of suppliers who offer cashback to quidco members.
To get the cashback you have to click to the suppliers website via the quidco website
Quidco then tracks your purchase and collects cashback for you which it holds in a sort of bank account
You set an amount which is then paid to you when you reach it
If the supplier messes you about then you log a complaint with quidco
If the supplier messes too many members about then they block the supplier