Who is your ISP? They may provide you with a free modem/router.
If not, the sort you buy will depend on whether your ISP connection is DSL (Virgin Media) or ADSL - any other provider.
You do not need to pay anyone to make the wireless connection secure. By being patient and following the instructions you should be able to do it. When the time comes and you are ready to give it a go, there are many people here who will give you a hand.
A dongle is a USB wireless adapter. If your laptop or pc is not already wifi enabled, you plug the dongle in and it receives the wireless signal.