Here's another way. Center the star. The time in seconds, divided by 120, equals the diameter of the field in degrees. An example is shown in the photograph here. By sliding these circles across the charts, you can see exactly what star patterns will pass through your field of view when you sweep across the sky.
Beginners are always surprised at how tiny the view really is.
Now we're ready to go on our first deep-sky hunt. Any observing session should begin with some indoor planning. Let's use Gemini for a dry run. If you know the constellations, you can find its two bright stars, Castor and Pollux, in the sky. These will be our starting point.