This is something that we have been asked directly several times and is very simple, I’ll explain it in 3 simple steps.
1. – Make sure your Mac is running OSX Lion (10.7.2 and up).
On your Mac, go to the upper left corner and click on the Apple logo.
Click on where it says “About this Mac” and under the big Apple Logo there’s the Mac OSX version.
2. – If you Mac has OSX Lion then we go to System Preferences.
In the first column from left to right in the third row is the iCloud panel.
Click, type your Apple ID and password.
Enable the options that you want and done!
3. – To enable iCloud in applications like iPhoto and iWork just open the application. (Only if you enable the Photostream and Documents on iCloud panel first)