Check the video on how Quidco works:
Basically, You will shop from the individual websites, like Zavvi. If you click Zavvi's link on Quidco, you will go to Zavvi's website for shopping. Quidco will get a commission from Zavvi for directing you towards them, which Quidco will share with you.The money is directly paid into your bank account after 4-6 weeks of that transaction.
They charge £5 per year, which is only taken from you if you earn more than £5 for that year.
I've earned about £550 from Quidco (for things I would normally shop online) in the past two and a half years.