An apprenticeship is a, usually, paid placement with an employer in which you are taught many of the skills required for that particular trade or profession. It is pretty much a 'learn on the job' job in which you are often attached to an experienced member of the team.
Apprenticeships were huge a while back in the trades, such as carpentry or building, but began to tail off until recently due to employers cutting back on expenses. After all, why would you want to spend time and money training someone if there was already someone with the existing skills you could employ. A Government initiative to reintroduce apprenticeships boosted numbers again and there are plenty of apprenticeships available in both manual and non-manual trades.
Apprenticeships are an excellent way of getting into an industry. You are usually paid whilst you learn, you get to learn in the environment in which you are working and there is often a job for you at the end of it as employers would be keen to reap the benefits of their training.
A good apprentice should have a number of attributes to make him employable in the first place, valuable during the apprenticeship and employable after the end. They should be passionate about the subject in which they are apprenticed, should be keen and eager to learn as that will make the entire process better for all concerned and they should be prepared for a lot of hard work, because employers would want to make you the best worker you can be.