In Calendar app, I clicked the + button to add an event. When I'm done filling all the event details out, I click the blue Done button in upper right corner. It adds my event but it won't leave the Add Event page. I'm stuck on that page whenever I'm in the Calendar app.
This problem likely can be remedied by restarting the app (Double Tap the home button, tap and hold the calendar app icon until an X icon appears, tap the X icon). If that doesn't work, I would reboot the phone (hold the power and home button down until you see the Apple logo).
If this doesn't help, I would recommend posting screen shots.
Here's an easier way: hold down the power button when this happens, but don't turn off the device. Hold the home buttom until your calender app unfreezes. You should still have the event in your calender after that!