A fine is an amount of money that a court may order you to pay as a penalty for committing an offence. A fine may be the whole sentence (penalty) or just part of the sentence you receive for the offence. The court normally has a choice about how much the fine should be when it sentences you.
An infringement notice is issued for a minor breach of the law, where it is not serious enough to need to go to court (they are sometimes called 'tickets'). This could be something like a minor traffic or parking offences. Infringement notices can be issued by the police, a local government authority (the shire or council), or other prosecuting agencies. The penalty under an infringement notice will be the same amount for everyone who commits that offence.
A fine can only be imposed on you by a court. An infringement notice does not have to be issued by a court in order for it to be valid.
There are different rules for dealing with fines and infringement notices, including how to dispute the amount and exactly what can happen if you do not pay the money. You can lose your driver's licence if you have unpaid fines or infringements, which can lead to even bigger problems with your job, your finances, the police and the courts.