If it's just a matter of moving back and forth, how complicated can slide show navigation be, anyhow? Well, it's more than that. Navigating often means finding a slide that's farther away than the next or previous one. And sometimes the Next and Previous commands don't move you directly to the next or previous slide.
The prime example is when you have animations on a slide. Say you have a bulleted list that is animated to fly in, line by line, each time you click the mouse. You must click through (or press N for each line) the animated list before a click goes to the next slide.
You'll have a similar experience when you click Previous or press P to reverse: In the animated list, the items will fly out, disappearing one by one, until you click through the list. Only then can you click to the previous slide. (Click Play on the left to see an example of this.)
It's critical, then, that you have a way to go directly to a specified slide without relying on clicking or pressing N and P or other step-through methods. Pressing the slide number and then ENTER is one quick way. The next section details this and other shortcuts.