There are various types of workplace agreements.  The relevant ones are workplace agreements between the employer and the individual employee and workplace agreements which cover all employees in the business or a specified group of employees.

A workplace agreement is different to a common law contract of employment in a number of important ways:

A workplace agreement is a formal written document which must by law contain certain terms.
A workplace agreement must be formally lodged with an authority.
A workplace agreement can be inconsistent with an award so long as the employee is not at a disadvantage overall.
Specific documents must be completed before a workplace agreement can be lodged, and failure to do so can lead to penalties.
Specific documents must be given to the employee to read outlining their rights at law before a workplace agreement can be lodged, and failure to do so can lead to penalties.