Australian Travel is intended to help individuals and legal entities in their administrative travel paperwork. To apply for an ETA online (VISA for Australia) you must be outside Australia and intend to visit for tourism or business visitor activities.
(Electronic Travel Authority) is an authorization to enter Australian territory, and is electronically linked to your passport. Australia ETA is for short term stays for tourism or business visitor activities.
Business visitor activities do not include work.
If you want to do short-term, highly specialised, non-ongoing work in Australia, you can apply for a Temporary Work (Short Stay Activity) visa (Subclass 400) in the government site.
What do you must know?
ETA authorization is valid for 12 months from its date of issue or until your passport expires, whichever is earlier. During this time you can get in australia whenever you want.
To apply for an ETA online you have to be resident outside of Australia.