While pressing W is the easiest way, I want to show you how to access the View menu, as you're likely new to InDesign. From the View menu, you can make other changes to how your document appears on your screen.
(An important option to note is Display Performance, which changes how much processing speed it requires for your computer to display the document preview. A lower setting will make your image blurrier but easier to display, for example.)
- Go to View in the top toolbar.
- Go to Screen Mode.
- Select either Preview or Normal.