With the iPhone, WYSIWYG. There are no hidden features. With Calendar, you can enter 2 alerts for an vent. After setting the 1st alert, you get an option for a second. These are at specific time intervals - 5, 10, 15, 30 minutes, 1, 2 hours, 1, 2 days - before the event. There is no snooze option.
The User Guide is your friend for learning how to use iPhone features. It's bookmarked in Safari for the iPhone formatted version, and:
http://manuals.info.apple.com/enUS/iPhone_UserGuide.pdf
(see pages 94-96)