There are three types of events:
Appointments - appointments have a start time and duration, and appear on your calendar.
Deadlines - deadlines can be all-day events or have a cutoff time. All-day events will appear on the top part of your calendar, while deadlines with a cutoff time will appear on your calendar at the cutoff time.
Tasks - tasks are similar to deadlines. Tasks can be all-day events or have a cutoff time and will appear on your calendar similar to deadlines.
You can create an unlimited number of reminders for an event either when creating the event or when you edit it at a later time.