Capital Gains Tax is the tax on the profits from the sale of an asset. The ATO has plenty of information on the treatment of Capital Gains Tax and how to apply them.
It is a complex transaction to get right. People who end up with a capital loss may forget to register the capital loss as the accountant will still charge to add this in. Your capital losses will roll over each year until it's applied against a similar asset that gets sold for a profit.
If you decide to sell an asset, such as real estate or shares, you usually make a capital gain or a capital loss. The capital Gain is the difference between what the asset costs to acquire and what you receive when you dispose of it.
Original post by the ATO at https://www.ato.gov.au/general/capital-gains-tax/