A program makes a computer usable.Therefore, it is necessary to instruct the computer to:

accept a number representing the distance;
accept a number representing the travel time;
divide the former value by the latter and store the result in the memory;
display the result (representing the average speed) in a readable format.Contemporary computers can only evaluate the results of very fundamental operations, like adding or dividing, but they can do it very fast, and can repeat these actions virtually any number of times.For example, a computer cannot understand the value of a complicated mathematical function by itself, although this isn't beyond the realms of possibility in the near future.Similarly, without a player, a piano is nothing more than a wooden box.