Shows Different Contents When Click Different Buttons

Currently I have one php page with an iframe in it. There are buttons in the parent page that links to different contents, all targets to the iframe.

Now i want to avoid using iframe and I think I can do the same thing (showing different contents in one specific area) through using a few of javascripts, except that I almost knows nothing about javascripts.

Anyway, my page is something like this:

PHP Code:

I am thinking about using php code like include() together with some javascript.