To get the Zoom tool in Photoshop and Elements, press the letter Z on your keyboard. Check the tool options bar at the top of the screen (or bottom of the screen if you are working in PSE11.) If the Magnifying glass with the + is checked, you are set to zoom in. If the Magnifying glass with the – is checked, you are set to zoom out. With the zoom tool selected, just click your document to zoom in or out.
When you are working with the zoom tool, you often want to zoom in to check a detail or perform a task, but then you’d like to zoom back out. You can quickly reverse the function of the zoom by holding the Alt key (Mac: Opt key) as you click. When you release the Alt/Opt key, the tool reverts back to the original direction, saving you the trouble of making changes in the Options bar.