Source: https://www.commsec.com.au/education/learn/managing-investments/how-do-franking-credits-work.html
Case study: James receives a tax refund
James owns shares in a company. The company pays him a fully franked dividend of $700. His dividend statement says there is a franking credit of $300. This represents the tax the company has already paid. This means the dividend, before company tax was deducted, would have been $1,000 ($700 + $300).
Come tax time, James must declare $1,000 (the $700 dividend plus the $300 franking credit) in his taxable income. If his marginal tax rate was 15%, he would have paid $150 tax on the dividend. Because the company has already paid $300 in tax, James will receive a refund of the difference, which is $150.
If James was in a higher tax bracket he may not have been entitled to a refund of any of the franking credit, he may even have to pay additional tax. However, if he is a low income earner, it is possible to be refunded the full amount of the franking credit.
Visit the ATO website for more information on dividend imputation.