12 o'clock Noon is when the sun is directly North/South/overhead, but not East or West any. But because it would be impossible to keep appointments if everywhere kept its own local time, we break geography into big chunks called "time zones." Everywhere in that zone agrees to use the same time, which is about correct for the middle of the zone, and is exactly one hour offset from the zones on either side.

Because the sun is over the east before it's over the west, the eastern zones experience things like sunrise, local noon, and sunset before zones to the west. So, if local noon is 12o'clock, then by the time it's 12 in the central zone, it's already 1 on the east where local noon happened an hour ago.