I would like to know what's to be done at the approaching of a probationary period. Should a form or a letter be sent to the supervisor? Any examples please.
Thank you

Don't send them a letter. They know when your probationary period is up and will notify you if you have not met their requirements as an employee. The supervisor may or may not come and tell you that you've passed their requirements. Keep showing up at work until you're told not to and you've got the job permanently.