Heuristics or Heuristic value(s) are the approximations for your problem to reach the answer(goal). Let's say you have an algorithm that finds the shortest path from point A to Z. Now, if you go by predictions you may get lost as there're several other points in between your start & final position.
For an analogy, let's say you are traveling in a city, you don't know anything about the routes. To reach a certain place in that city, what you will do, you keep going on & on by taking advice from the people around you. Now, the time in which you reach the place depends on the quality of advice that the person gives to you.
Now, let's relate it. In the analogy, you is your algorithm that is trying to reach a certain place (goal) & the heuristic value is the advice of the person. Same as in the case of your AI algorithm, the better approximation (heuristic value) you have the less in time you reach your problem goal.
Hope it helped!