The heating curve diagram shows the process of water being heated or cooled. For instance if you have water frozen at -10 degrees celsius and heat it to 0 degrees celsius it will stay at 0 degrees until it is completely melted. Then the water will stay liquid until you raise the temperature of the water to 100 degrees where it will start to evaporate and that will create water in the evaporated state called steam. Then that steam can be heated and it will not change the state of it. Short video of how its done!
The graph is easy to show how much energy is needed to heat a substance to a certain temperature. You need to make sure that when you are going from a negative temperature to 0 degrees you need to make sure you use the formula Q=mc∆t and then when you reach the flat line use the formula Q=mHf because there is no change in temperature. Then the next formula is Q=mHv and then then you will use the first formula you used to find how much heat it takes for the last slope. Then you use the formula Q=mc∆t.Then the next formula is Q=mHv and then then you will use the first formula you used to find how much heat it takes for the last slope.

An everyday example of using this method would be boiling water, melting ice, ice turning into water.
(Something to try)
Take some ice and put it in a pan on the stove. Then turn the stove on and watch the ice melt. You know now that when the ice melts, its at 0 Degrees C. Then its just plain water. As time goes on the temperature goes up, so then the water starts to boil. You know that the water is now at 100 Degrees C. You can see the water turning into water vapor and rising into the air.
wiki video
Units that will be used in the equations will be J/g and J/g Degrees C
example:
How much energy whould it take to raise the temperature of 20 grams of ice at -40 degrees celsius to 125 degrees celsius.
Q=mc∆t
Q=20g x 2.065J/g°C x 40
Q=1652J/g°C

Q=mHf
Q=20g x 334J/g
Q=6680J/g°C

Q=mc∆t
Q=20g x 4.18J/g°C x 100
Q=8360J/g°C

Q=mHv
Q=20g x 2260J/g
Q=45200J/g°C

Q=mc∆t
Q=20g x 2.02 J/g°C x 25
Q=1010J/g°C

1652 + 6680 + 8360 + 45200 +1010= 62902