You can create and update calendar events directly on iPhone.
Add an event: Tap and enter event information, then tap Done.
You can also touch and hold an empty spot on a calendar to create a new event. Drag the grab
points to adjust the event’s duration.
Set an alert
Tap Alert, then set an alert from 5 minutes to two days before the event.
Set a default alert for events
Go to Settings > Mail, Contacts, Calendars > Default Alert Times
Update an event
Tap Edit and change event information.
To quickly adjust an event’s time or duration, touch and hold the event
to select it, then drag it to a new time or use the grab points to change
Delete an event
Tap the event, tap Edit, then scroll down and tap Delete Event.
Invite others to an event
Tap Invitees to select people from Contacts. This requires an iCloud, a
Microsoft Exchange, or CalDAV account.