If you're going to work in a licensed premises (that is, a place that sells alcohol), you must complete competency training in the Responsible Service of Alcohol (RSA). If you don't have valid evidence that you've completed the RSA training required for working in a licensed premises, you could be fined.
You'll need to be trained by an approved training provider. You can find an approved training provider using Liquor & Gaming NSW's online search and mapping tool.
Once you've completed your training, you'll need to apply for an RSA or RCG competency card if you don't already have one.