Q: no icloud on my mac

You need Mac OS X 10.7.5 or later for iCloud.

The current version of Mac OS X is 10.9.2

What version is yours? Check by choosing About this Mac from the Apple menu.

Read this:  iCloud: System requirements

OT

You need to go to  > About This Mac, then read the Version number as in the image below:

iCloud on your Mac requires OS X 10.7.5 or later.  If you have 10.5.8, you would have to have purchase a Mac OS X 10.6 DVD from the online Apple Store, then get the 10.6.8 combo installer: (http://support.apple.com/kb/DL1399).  Once you have 10.6.8, you would have to either download Mavericks from the Mac App Store (system requirements here: http://support.apple.com/kb/HT5842) or, if your system can only run Lion, you can go here to purchase a redemption code to download it from the Mac App Store.

Before doing anything, make sure your Mac at least meets the system requirements for OS X Lion:

• Mac computer with an Intel Core 2 Duo, Core i3, Core i5, Core i7, or Xeon processor
• 2GB of memory
• OS X v10.6.6 or later (v10.6.8 recommended)
• 7GB of available space

If it doesn't, you won't be able to use iCloud on your Mac.  Before upgrading, you may want to check the compatibility of your existing applications by checking here: http://roaringapps.com/apps:table.   Also be aware that older PPC programs such as AppleWorks and Office 2004 for Mac will not run on OS X Lion or higher.

With an iMac8,1 you can run Mavericks.  However, you'll need to have 4 GB of RAM.

It's easy to install RAM in iMacs. I've upgraded several without a problem.  Go to Crucial.com and check to see what you can upgrade you iMac to and it's cost.  Crucial is much, much less expensive than Apple memory and is a very good supplier.