via the internet you must have a Radio broadcasting licence. You won't get this until you have attended a course of instruction and passed an exam. In the UK there are three licence levels for amateur broadcasters, and you must start with what's called a foundation licence.
If you want to broadcast music you'll have to pay the Performing Right Society for a licence as well.
Technically and financially this is a pretty challenging thing to be contemplating - are you sure that you want to do it? If the answer's still 'yes'