How to sync iCal between my iMac, iPad and iPhone? I get duplicate entries

I have a university Email (with Calendar) and then iCal on my desktop, laptop, ipad and iphone. I am finding that my calendars are not synced at all.. Either I get duplicates or I only get what I put on specific device.

BTW- I do NOT have On My Mac calendars checked..

--

is it easy to fix on my own or do I need to get to a Genius at an Apple store?