The term clockwise describes the direction in which the hands of a clock move. Looking at a clock from the front or above, the hand of a clock moves right and around in a circular motion. With reference to the numbers on a clock, they are passed in order from least to greatest, starting from 12, which is the 0 position of a clock. In the image below, the arrows indicate a clockwise direction:
Both the terms clockwise and counterclockwise are defined based on looking at the clock from a specified direction. For example, looking straight at a clock on a wall is one possible direction. Another possible direction is a person standing on the other side of the wall. If there were someone else on the other side of the wall who could see the same rotation that we were looking at, from their perspective, a clockwise rotation for us would be counterclockwise for them.
Another example is the rotation of the Earth. The rotation of the Earth is clockwise if viewed from above the South Pole, but counterclockwise if viewed from above the North Pole, where "above" means farther away from the center of the Earth.
Although the term clockwise originated with the use of clocks, it is also used in other areas. For example, many objects such as jar lids, screws, bolts, bottle caps, nuts, and more, need to be turned a specific direction to be tightened or loosened. They are usually designed to be tightened when turned in a clockwise direction with respect to the person looking at the object, and loosened when turned counterclockwise. This is because more people are right-handed than left-handed, and it is generally easier for a right-handed person to tighten a screw clockwise than counterclockwise. There are special cases however, where clockwise rotation loosens, and counterclockwise rotation tightens.
In coordinate planes, angles are usually measured counterclockwise, starting from 0°, which is on the right-hand end of the coordinate plane. You can think of the direction as east.
In certain games where players take turns, such as board games, the turn order often proceeds in a clockwise direction. This can depend on area however, and some regions and countries tend to have turns or gameplay proceed in the counterclockwise direction. There is no real rule or reason that one particular direction should be used over the other, and it is mostly a matter of custom.