If you do photo retouching, very often you will zoom very closely into a particular part of the image. Similar to what you see above.
To move around the image, you can hold down the Space Bar and then drag the image around.
Holding down the Space Bar will temporary switch to the Pan Tool.
Upon releasing the Space Bar, Photoshop will revert back to the original tool that you were using.
This is a good way to move around the image and it is still the most common method used by Photoshop users today. However, there is a feature in Photoshop that will give you a temporary Bird's Eye View of the entire image.
To use this feature, Press and hold the [H] key on the keyboard and then click the mouse. Photoshop will zoom out and a rectangle will show you the area that you are currently zoomed into.
Move the rectangle where you want to zoom into and then release the mouse button. All this time, continue to hold down the [H] key on the keyboard.
Upon releasing the mouse button, Photoshop will zoom into the selected area.
Try it out and experience it for yourself!!