I wanna to have a look at a simple CMS coding that can be use for my general studies in PHP. If you know any, please let me know.

Well when you say simple do you mean this simple?
eSite
That is REALLY simple, there is a tutorial on PHPClasses but you have to be signed in to use/see it so i could copy it but I'd mostly likely get myself in trouble so ill give you the link, sign up and look at it yourself!
Read this First
This is the actual CMS but look above for the bit you really need to learn!

It does not use MySQL, if anybodu knows the one with usage of MySQL?

Take a look at http://www.opensourcecms.com/ . They list pretty much every CMS available at the moment, along with descriptions and demonstration versions running for you to take a look at. Look in the Portals (CMS) section in the menu on the left and go through the various CMSs available, pick one you like the look of, download the source code and then take a look at the code that runs that CMS. They're all different, so take a look at a few. Also, use the online demos. If you spot a feature you like the look of, see if you can work out how it is done by looking through the code.

Thanks, but I think their code are not for beginners?!

you can search at www.pscode.com. the site has php codes for all learners from beginners to advance

Oh, thanks. What is about e107? Is it a simple cms system?