How can I make pictures from thumbnails become bigger when clicked with some coding?

I am in the process of creating a website and I want to have a small gallery with pictures. The thumbnails would be very small and I would like them to open up when people click on them but I want it to be on the same page I don’t want them to open in a new page. Here is an example of what I want: http://www.thegnomonworkshop.com/store/product/928/Stylized-Character-Modeling-for-Production
On the right where it says DVD Stills gallery.
How complicated is this? can someone help me with some code or the basics?

Thanks!