In Germany we have a time change twice a year. The summer time begins on the last Sunday in March. There you put your clock one hour forward from 2 am to 3 am. On the last Sunday in October you
put it back again from 3 am to 2 am. This happens across Europe. It was introduced in 1980. A main reason was to have a better use of the daylight and save energy.
You want to know what time it is in your hometown to call your family or friends? The World Clock or the World Time Zone will tell you.