Essentially, economics is based around the entire economy, while business studies is based around individual firms.
I only did economics, not business studies, so I'll try and give a brief outline.
HSC economics deals with four main areas - aspects of globalisation, the relationship betwen Australia and the global economy, economic issues and economic policies. Economic issues include areas such as inflation, unemployment and the environment - while economic policies are things such as government budgets and monetary policy which aim to control and/or influence these economic issues.
I found economics enjoyable because it isn't just about numbers and statistics (even though these are still necessary). A large part of economics is based on your own perspective, and how well you can evaluate the effectiveness of current policies in addressing issues that currently face the economy, such as the GFC or the threat of increasing unemployment.
Cause and effect also play a large part in economics. For example, unequal distribution of income is increased through the regressive taxation of the GST, yet progressive income taxation reduces income inequality. Better income equality increases consumption of goods and services because low-income earners now have more disposable income, which may help stimulate the economy, but may also cause Australia to become reliant on imports if domestic firms cannot produce enough goods and services to meet demand.