These simple steps will explain how to mask out an image to take upon the shape of text.
Step1. Open the image of your choice and then duplicate the layer. Next, type the word you want across the image as shown below.
Step2. Move cursor over the layer with the type icon in the layer box. Hold control or open apple and then click. You should now have the marching ants around the text.
Step3. Turn off the original image layer and the text layer. Select the duplicate image layer in the layers box as shown below. Finally click on the add layer mask icon at the bottom of the layers box to clip out the image.
Hope this helps!