Actuaries apply their statistical and mathematical expertise and knowledge to the financial world. They look at what's happened in the past and use it to make predictions about the future, developing business strategies which are appropriate given the risks involved and their probabilities of occurring.
The mathematicians and economists can, of course, suggest all sorts of models and approaches, and there are specialist IT actuarial packages which make traditional number-crunching tasks less time-consuming. However it is the actuary who will need to choose the specific methods and data to use, so as to be able to stand by the results and accept the real-life consequences of them being wrong. So the actuary is very much a person of judgement rather than one who simply applies technique. Correspondingly, actuaries will usually have a responsible, senior and well-respected position in organisations.
To qualify as an actuary, a candidate must pass a set of professional examinations. There are several papers covering many areas. Exemptions may be available from some of the papers, depending on a candidate's previous qualifications.