What is the basic economic problem?

To answer this question, one must take into account the varying schools of thought which exist in economics (neoclassical, Keynesian, Marxian, behavioural, feminist etc.). However, for GCSE and A-level Economics, the primary approach will be the neoclassical (mainstream) one and thus, this should be your focus.
To put simply, the basic economic problem is that individuals have unlimited wants yet have limited resources to satisfy such 'wants'. This idea is supported by two key economic concepts: scarcity and opportunity cost. 'Scarcity' can be defined as the finite nature of resources. Thereby, choices have to be made to satisfy the wants, which we most greatly desire. This leads to an 'opportunity cost', which can be defined as the cost of the next best alternative. To really excel, one can take it a step further and consider how an economy may solve this basic economic problem. The economist Paul Samuelson simplifies this best, concluding that an economy must answer three fundamental questions: What to produce? How to produce? For whom to produce?