Under Migration Act 1958 (Cth) and Migration Regulation 1994 (Cth), a valid visa is required to enter and remain in Australia. A non-citizen who is in the migration zone and does not hold a valid visa is called an unlawful non-citizen. An unlawful non-citizen must be detained and removed unless they have or are granted a visa. There are more than 100 different visas and each visa has its own validity and eligibility criteria. The defined criteria must be met for visa to be granted. The visa officer must be satisfied that you have a genuine intention to visit Australia under which category the visa has been applied.
Once the visa is granted every visa holder must adhere to their visa conditions during their entire stay in Australia. Strict penalties, visa cancellation, deportation, removal and exclusion period may apply to those you do not adhere to these requirements. You can check your visa entitlements, such as work rights, health requirements etc. using the online service called- Visa Entitlement Verification Online (VEVO).