Economics is typically the study of and measurement of financial transactions over a large area and population. Financial transactions typically include the exchange of goods and services often using currency or money as medium of exchange.
The word economics itself comes from the Ancient Greek word oikos (οἶκος ) which means 'home or dwelling' . (oikos, "house") + nomos (νόμος) , "custom" or "law")
Which all comes down to household management. This means organising how things around a household are managed. Stretching this to larger scale it is about managing who does what and for how much in an entire society.
A collection of coins or currency represents a form of money; an important aspect of economics. image: wikimedia.org
The study of economics now considers more specific areas which vary in scale and scope. For example microeconomics and macroeconomics. It also looks at different styles of economies or ways of looking at economics from a philosophical perspective.
How economics is studied is rather varied due to so many wide opinions. One way of understanding this is the use of positive (what is the economic behaviour of a region) and normative economics views (how economic behaviour should be).