What is tone mapping?
Tone mapping has to deal with the image contrast.
You can make a single exposure look like a HDR image. There are many ways to use tone mapping, I use it to bring out detail in the image.
As you see from my example below, the before image is flat, dull looking. I then used Nik Efex Pro tone mapping filter and increased the contrast, thus increasing the detail. It is more fun to play with than it is to explain.