Can someone explain in very simple words what it is? Also, provide an example. So for example, if u have to find the heuristic function of something how is it supposed to look like?

Take as an example of the problem:

For the water-jug problem __http://www.math.tamu.edu/~dallen/hollywood/diehard/diehard.htm__

Devise and explain an admissible heuristic function (h) [not the trivial h(n) = 0]. The cost of an action is defined as 1 unit for performing the action, an additional 1 unit for moving each gallon of water (fill, empty, pour), and an additional 1 unit for wasting each gallon of water (empty). The path cost (g) is the sum of the cost of all the actions.