The UK system (PAYE - Pay As You Earn) has the Inland Revenue provide a code to your employer which tells them how much tax to deduct each month. If your tax position changes during the year, the code is changed, and the adjustments are made automatically on future salary payments.
Australia's system is similar for employed people, except that the code adjustment is voluntary. Your employer deducts income-tax from your salary according to the amount you are paid, and at the end of the year issues you with a "Group Certificate" (in the UK it is a "P60", I think?), which you submit with your tax-return. If you have a tax-deductible expenditure (interest on certain loans, for example), you
can apply to the
ATO, and have it deducted from your PAYE payments, but many employees don't want the company pay clerks to know their private financial affairs and so don't do this*, but instead claim back at the end of the year.
*In Australia, mortgage (home loan) interest payments on your own home are
not tax-deductible, so having deductible loan-interest implies that you are engaged in "negatively geared" investment in property, shares etc. which has at times been politically controversial as a form of tax-avoidance by high-income individuals.