Tax offsets are also called rebates. 
Generally, Tax offsets help to reduce the tax payable amount to ATO on your occupation related taxable income.
In addition, Tax offsets can reduce your tax payable to zero to ATO, but on their own they can’t get you a refund. But it’s depends upon case to case.
You can get more information which links below about offsets and rebates:
- Private health insurance
- Australian Government allowances and payments tax offset
- If you maintained an invalid or invalid carer
- Low and middle income earners
- Medical expenses
- Seniors and pensioners tax offset
- Super related tax offsets
- Zones and overseas forces