Howto display webpages into 1 webpage(index.php/homepage)?

How do I display the other webpages into 1 webpage the index.php page for a website?

Instead of having page1.php, page2.php, page3.php,… pageN.php
I want to have a ‘function.inc.php’ with all the webpage codings
and use index.php (homepage) to display them within it body.
Buttons will be created on the homepage for each page, and when
it is clicked the function for that page is displayed on the homepage.

I am using tables to create the homepage, so the buttons will be in
the table row to the left and when any button is clicked the function is called
and display in the table center row.

I think this method will use less web space.