STEP THREE – CREATE A NEW LAYER AND TYPE SOMETHING
Using a font that is like Impact or Arial Black with straight edges and thick works best for this effect.
Go to the Edit menu > select Transform and make text as big as desired, by dragging on the handles. If you hold the shift key down whilst dragging on the handles, the text will re-size proportionately.
Obviously the bigger you make the text, the more of the underlying background image you will see.
STEP FOUR – DUPLICATE YOUR BACKGROUND LAYER (CMD/CNTRL J)
Move the duplicated background layer above the text layer.
Right click on duplicated copy layer and select create clipping mask.
STEP FIVE – TURN ON YOUR WHITE FILL LAYER
Click on the eyeball and there you have it, your image is now inside your text.
You can play around with the solid colour layer (in this case white) by selecting that layer, changing the foreground colour and pressing alt backspace (win) or option delete (mac).