depends if you apply for undergraduate or postgraduate
if its undergraduate apply thru UCAS. applications should be made a year in advance. there is a fee to pay for that too - not much though. you can select up to 5 uni (depends on the course/ for medicine its 4 i think, or else its 5-6 normally)
if apply for PG, for most apply directly to university, they have application forms on their own websites
