You can save your application midway through completion and come back to it later, if required.
To do so look for a link or button on the page that says either "Save and continue later" or "Save and exit application", depending on which part of the application process you are in.
When you're ready to continue your application simply return to the applicant portal (https://myportal.accuratebackground.au/login), login, and you will see a button that says "Continue" next to your application listing.
Click this button to continue your application from the point at which you saved it.