An offer of employment and the contract of employment should always include an initial probationary period, typically of three months, if allowed under local labour laws.
The purpose of a probationary period is to allow both the staff member and the organisation to decide if the right person is in the right job.
During a probationary period, either the staff member or the organisation can terminate the employment with less notice and justification than after the probationary period.
Performance appraisals during the probationary period can identify assistance the team member needs to perform, and help the organisation to decide whether the team member's performance is satisfactory.
At the end of the probationary period, the contract may have to be confirmed in writing or may come into force automatically depending on how the contract is written.
Do not wait to the end of the probationary period before considering whether performance is adequate, and then delay confirmation of the contract while making a final decision – it is unprofessional and unfair