A dongle is a USB stick that enables you to use the internet where ever and when ever on your lap top .
There are many phone companies that sell it on a contractual basis along with a free laptop . We Bought ours from Phones 4 you and it was with Orange . We pay £30 a month ( a little bit less at the moment with the Vat being at 15%) and you can use the Internet all the time for no extra cost - you have certain amount of megabytes that you can download per month and if you exceed this you will be charged like you would a mobile phone contract but obviously there is different options for the amount that you down load .
We opted for the basic package as it was mainly for surfing the web and iTunes etc . we have downloaded various things but so far have never gone over our limit and you can check on line with Orange how much you have left if you were worried. The only down side is with Orange is that its uses 3G as your signal so sometimes its slower than others but overall we have never had a problem with it bar having to unlock the Child protection on it but to be fair I think that is a good thing that it was on to start with as the companies never know who will use the laptop !
Before we got it we had debated getting broadband but we are glad we opted for this instead as its saved so much hassle when we moved house - it just came with us and all we had to do was change the address. No Problem .
You can buy just the Dongle and not the lap top which is Cheaper but you still have to buy a contract which is usually 18 months and the prices start from about £15.00 or if you wanted it for a present for a child you can get prepay dongles - again like a phone - you put credit on it . My Aunty uses this option and she was surprised at how long the credit lasted .
I would recommend to anyone to get a Dongle