Help with iphone/iPad calendar

[Jemster]

I'm rubbish at technology stuff. I want to be able to link the calendar on my iPhone 5 with my iPad mini so they update each other automatically. How do I do this?
Also I seem to have several calendars set up some are under Yahoo & some under ICloud. Which should I use or doesn't it matter & can I delete all the others as I'm currently getting confused as to which one I'm using!
Thanks for any help

If you go to settings and iCloud settings it will give you a load of slide options to choose what you want to sync between different devices by iCloud. Make sure your calendar is on and as long as both devices are connected to the same iTunes account they will sync.