CMS Made Simple Forums

Where do I change the images and the text in that slideshow?

There's a template called "Simplex Slideshow" that creates a Smarty array for the slideshow. It's probably not the easiest way to do a slideshow for a beginner, but isn't too hard to figure out.

There are modules and many other ways to do a slideshow. Personally I tend to use the Gallery module and create a template using either something available to my framework (Bootstrap/Foundation/etc) or a third party slider such as bxslider.

As well as Gallery consider an even more plug-and-play option, the Showtime2 module, which is responsive if you need it to be and also has an easy to use interface.
http://dev.cmsmadesimple.org/projects/showtime2