How to load external example.php into index.php(div ="content")

How to load external example.php into index.php(div ="content")

Hi mam/sir.

I'am a jquery beginner. 
and making my first site project.

I just want you to ask some question. 

Can you give me tutorial or example code
How to load an external download.php into index.php(div ="content")

example..

This is tab navigation

Home Download About Suggestion

Then If I press Download Button i want it to load in Home (div="content")...

Hope you can help me sir.. Thanks.. :))