Dear Webdeveloper.com readers!

My name is Keifi, and I'm dutch. I just started my website www.zoveelkorting.nl and I'm doing kinda great.
This only one thing I'm stuck on.

I want to make a button that whenever someone clicks on it a ''couponcode '' reveals in the button.
For example like this one. http://www.vouchercloud.com/bhs-vouc...t-voucher-code

When you click on '' Get code'' the webshop opens and the code reveals in the button. This is exactly what I want.

How can I make this? Your help is much appreciated!!