I will start this tutorial by saying that I am not a Photoshop master so I get a little confused sometimes; for example in this tutorial I will explain for all the Photoshop beginners a quick way to enhance a photo by using a Gradient Map. As you will see if you open the fill or adjustment layer tab we have to gradient options: the Gradient (Fill) and the Gradient Map; so the question is which one to choose and use? And of course what is the difference between the two of them. For the first question I will choose the first option, the Gradient (Fill) instead of the Gradient Map. For the second question I have no answer.
Gradient Map and Gradient Fill Adjustment Layers
A Gradient Map is in fact an adjustment layer that can be applied to a layer/multiple layers and to enhance the image result. Learn more about adjustment layers from this tutorial.