How do I program Samsung Galaxy S4 to car so I can answer calls whilst driving? Can I do this through the steering wheel touch button controls??

No, you need an appropriately equipped head unit that has bluetooth functions in the head unit or aftermarket bluetooth package.

Neither the original head unit nor factory steering wheel controls have provision for bluetooth functions.

Neither the original head unit nor factory steering wheel controls have provision for bluetooth functions.
Yup. Because bluetooth equipped phones didn't come into play until 2000 and bluetooth car kits did not exist until 2001, your 1999 model car won't support it without an aftermarket headunit or bluetooth kit.

(source) (http://www.bluetooth.com/Pages/History-of-Bluetooth.aspx)

Thanks guys. Your help is appreciated. So the steering wheel button controls are only for stereo? What does mode stand for ?

I guess mode would be to switch between am/fm radio, cd.....