You can also use them when you take out house insurance, car insurance etc, just make the Quidco site your homepage on your browser and that way it will remind you to go through there every time.
It's really easy to use - create an account then every time you need to order something online do a quick search of the company you were going to use and see if they are on Quidco, if they are you click on their name and it takes you through to their own website, you then complete the transaction (making sure you still keep open your Quidco tab/window) then it automatically tracks the order and credits your account.
Sometimes the funds take a couple of months to come through but it's great seeing it in your account when you least expect it!