There are two branches of the legal profession in the UK: solicitors and barristers (advocates). The basic difference between barristers and solicitors is that a barrister mainly defends people in court and a solicitor mainly performs legal work outside court. However, there are exceptions in both cases.
How do I become a solicitor?
In England and Wales: The Law Society
In Scotland: The Law Society of Scotland
How do I become a barrister?
In England and Wales: The Bar Council
In Scotland: The Faculty of Advocates