I have heard that statement many times from new Mac users.
You will see forum threads like this one, http://forums.macrumors.com/showthread.php?t=154973
"does apple have a native image viewer like in windows? i like how in windows i was able to just click arrows to scroll through pictures, and i could slideshow easily."
The image viewer in Mac OS X is right there, in front of you. The Finder.
Just navigate to the Folder where you have your images, select all or some of them and hit the Space key.