Daylight Savings Time in the United States of America starts on the second Sunday in March of each year and ends the first Sunday in November of each year.
When it goes into effect each spring, clocks are moved forward by one hour at 2:00 AM standard time, and the time becomes 3:00 AM daylight savings time (DST). When DST ends in the fall, the clock is moved back at 2:00 AM daylight savings time, and the time becomes 1:00 AM standard time. This is where the saying "Spring Forward, Fall Back" comes from.
When on standard time, the time zones in the USA are Alaska Standard Time, Pacific Standard Time (PST), Mountain Standard Time (MST), Central Standard Time (CST), and Eastern Standard Time (EST).
When on daylight savings time, the time zones in the USA become Alaska Daylight Savings Time, Pacific Daylight Saving Time (PDT), Mountain Daylight Saving Time (MDT), Central Daylight Saving Time (CDT), and Eastern Daylight Saving Time (EDT).
Many other nations observe some form of daylight savings time, but not all start and end it at the same times as the USA does. Additionally, not all states in the USA support it. Arizona, Puerto Rico, Hawaii, U.S Virgin Islands and American Samoa do not.