When you travel east or west to a different country, you have to change the time on your watch. This happens because the Earth turns, so when it is daytime in some parts of the world, it is night-time in others.
We divide the earth into 24time zones, one for each hour of the day.All the places in the same time zone have the same time. We star counting from Greenwich, England. When it is 12 pm in Greenwich an travel east to a place in the next zone, Rome for example , it is 1 pm . If you travel west to place in the next zone , the Azores for example, it is 11 am.