A tradesman is a skilled manual worker in a particular trade or craft. Economically and socially, a tradesman's status is considered between a laborer and a professional, with a high degree of both practical and theoretical knowledge of their trade. In cultures where professional careers are highly prized there can be a shortage of skilled manual workers, leading to lucrative niche markets in the trades.
Wikipedia lists over 50 types of "trades" in the UK, so there are plenty of jobs going in this category! Cabinet makers to plumbers, electricians to plasterers - if you can specialise in a trade and drum up business in your local area, there's an opportunity to make some serious dough. Plumbing and Electrician professions are certainly more en vouge than 20 years ago, with many trade specialist making well over £60,000 per year.
Responsibilities and skills as a tradesmen really depend on the specific trade that you are involved in. A "Jack of all trades" is a slang term for someone with multiple skills and qualifications (the term initially applied to specific trades, but is now used more widely in society). An adept tradesman should be good with his hands, practically minded, will to work on his feet and fit as a fiddle.