Unless you are an Australian citizen or New Zealand citizen, you need to obtain a visa before travelling to Australia. The visa requirements for Australia are complex and change frequently, often three or four times a year.
So it is important if you are applying for a visa that you are aware of all the specific visa requirements that you must meet in order to be successful, if these are not met the visa cannot be granted.
If you lodge a visa application in Australia and it is refused, it may be difficult to lodge a further application if you do not hold a substantive visa as the Migration Act allows only a few such applications to be made.
So the general rule is that if you have had a visa application refused in Australia and you do not hold a substantive visa, you will need to go overseas before you can lodge another application.
People located living or working illegally may face serious consequences (including, detention, removal and exclusion periods from Australia) while employers of illegal workers can face fines and possible criminal charges.