This is raw data from measuring the heights of 20 students. Change the class width (interval size) and see how the frequency table and histogram change.
Listing out data one by one makes it hard to see the overall pattern. Split the range into intervals of equal width (the class width), count how many data points fall in each interval (the frequency), and put it in a table, and the distribution of the data becomes clear at a glance. A table organized this way is called a frequency table, and drawing it as bars gives you a histogram.
This way of organizing data comes up all the time in everyday life — grouping test scores into 10-point bands to see how many students fall in each range, or grouping the number of items sold in a day by time of day, are both examples of a frequency table.
Change the class width with the slider. Make the intervals too wide and the distribution gets blurred together; make them too narrow and the data looks sparse and scattered.