It is common practice for an employer to put employees on a probation period (or qualifying period) to determine if they are right for the role and organisation. Probation works both ways in that it gives you the opportunity to determine if the role is the right one for you also.
The most common time period for probation in Australia is six months. Although your job offer might include a different probation period. Make sure you are aware of the probation period before accepting a role.