I have a 56 plate Ford Fiesta and the stereo has an aux button which has never been used how does it work do I just plug lead in and it will?

As I said I have 56 plate fiesta and the aux button on the stereo is there but has never been used. If I plug an aux lead into my car where the USB port charger is will hat Work just by plugging my phone in and pressing the aux button or will it need something done to the stereo for it to work?

If your car has a factory original equipment radio, all the information you will need is written in the owner's manual that came with the car. READ IT!

Read the owners manual

It should work.
Try it or read the owners manual

Does your car have an aux port next to the power outlet - like this?

If not, you'll need to have one fitted.

I wouldn't have thought to ask anyone I would've tried it.

The head unit needs an aux input my friend.

Read your owner's manual. If there's no obvious aux jack right out front, you may need to install cables to it in the back of the stereo.

You should have an AUX input jack. The AUX input/button on my car allows me to play an iPad through the car's music system. The AUX button allows me to change to the radio without disconnecting the cable.