I hope you know the clearly about the INTERFACE. First I will explain with one real example.
Let us consider we are going to form a "ZOO". we are going to bring "Animals".
So we are going to create "Tiger" class. In the Tiger class we are going to specify all the habits ex. Eating habit, Walking hapit, Running Habit.
So we are going to create "Lion" class. In the Lion class we are going to specify all the habits ex. Eating habit, Walking hapit, Running Habit and going to create more animalis like this.
Here we can use INTERFACE. We should not miss the Eating habit, Walking habit, Running Habit of each animal's. and also we need the consistency in the naming of the habits.
So we can have one interface "IHABIT" it has the methods Eating habit, Walking habit, Running Habit. But it will be vary for different animals. Now while creating the any animal class we have to use that interface. So that the Interface force us to implement the habits.
This will help us not to miss any habits
This will help us to maintain the consistency of the habits
Direction is important than speed