set up for icloud on iMac

Greetings! Please let me know how MAIL should be set up on my iMac for iCloud. I have it on my iMac and iPad. I have been away and only using the iPad2. During that time, I had an upgrade to the new IOS6 system. Upon my return and using my iMac, I suddenly noticed that the Mail was not working properly for the iCloud account. Have there been changes in the interim? Anyway, I want to make it correct. THANKS!