Should you make a formal appointment to speak with the manager?
If what you need to say is important or you want a manager's
undivided attention, a formal appointment is best. If you have a
confidential matter to discuss--for example, you want to report
wrongdoing happening that affects the employer--you'll want a
private appointment.
However, sometimes ordinary, non-critical information can be
communicated in an email or short note. Depending on the business,
you can sometimes speak informally, say on the way to lunch or at
the end of the day.