Even if you are entitled to free health treatment, you may have to pay for your prescription medicines if you live in England. A prescription charge in England is currently £8.20 for one item (as of January 2016). If you are exempt you will not have to pay.
The NHS choice website has further information on prescriptions and also provides a list of the circumstances in which you would be exempt from paying these charges.
Prescriptions are usually collected from a pharmacy. For further details on pharmacies, please see the NHS Choices website.