Before the invention of time zones, each locality decided what time it was by setting "noon" to the time of day when the sun rose to the highest point in the sky. That worked well enough when life moved more slowly.

After the railroads connected cities and it became important to know to the minute when something was scheduled to happen, a difference in "noon" between your town and mine made scheduling extremely difficult. Time zones were established so that people all over a region could agree that 8:00 is 8:00, even if that meant the sun reached the highest point in the sky at 12:04 in my town on the same day it reached the highest point at 11:44 in your town.

An agreement like that works well for people up to a few hundred miles apart. Much farther though, and you'll have to convince people in the far west portion of the continent that the sun rises at 3:00 a.m. on the same day that the people in the east say it rises at 6:00 a.m. So they divided the continent into "time zones", each 15 degrees of longitude wide (which is what you get when you divide the planet's 360° by its 24 hour rotation period) as a compromise between everyone-everywhere-agrees-to-use-the-same-clock and everyone-gets-to-use-whatever-clock-they-choose.