A level means Advanced level and is normally a two year course. Advanced levels remain the Number 1 standard in the English system. Every university in the UK, in the USA, Canada and throughout the world will accept A levels as a way of meeting their entry requirements. To enter the best universities, students will normally require high grades in three A level subjects together.
A student taking a two year A level course would normally study four AS level subjects for the first year. After the first year, you would take the AS level exam papers in these four subjects in May/June. You would then continue with three of these subjects to A level, although exceptional students may take four.