Do you have a globe that you can look at? If not, use a ball or something round like an orange.

Take a lamp or a flash-light and turn it on and place it on a table where the light is shining toward the globe / ball / orange.

You will see that some of the globe is in the light and some is in the dark and if you slowly turn the globe you will see that the light and dark areas move.

This is what happened each day as the earth revolves - for part of the day we are in the area that is facing the light (the sun) and that is the hours of day-light and for other part of the day it is dark, which is night-time.

To make things easier we have divided the earth into 24 time zones that coincided with the 24 hours of each day.

As the earth revolves and it gets light, it becomes, for example, 6am in New York, then an hour later it becomes 6 am in Chicago, then an hour later it is 6am in Denver, then an hour later in Los Angeles.

http://www.worldtimezone.com/ this might help