Cashback sites will pay you when you go through them to make purchases online with other retailers. It's a great way to save a bit of money on things that you would have bought anyway. The way it works is that you sign up for an account on your website, and then say you want to buy a washing machine, or insurance, or a whole range of things, then first go to the cashback site, and follow the retailers links from there. The transaction will then be tracked, and a few weeks or months later you'll get some money added to your cashback account. 

Important things to remember: 

• Think of the cashback as an added bonus. Until the money's in your bank account, then you're not totally guaranteed to receive it.
• Withdraw the cash from your cashback account as soon as it arrives.
• Only use it to buy things that you were going to anyway, and hunt for the best deal. Sometimes this will mean going for an option where there's no cashback on it
   

Have a look at these, see what rates they're offering on the brands you buy from already, and see what works best for you:

Top Cashback. Quidco Kidstart