Between X-A water exists in a lattice formation where the molecules are in fixed positions showing minor vibrations. As the temperature approaches 0 vibrations become increasingly violent until the hydrogen bonds that hold the molecules in their fixed positions are disrupted.

Between A-B the ice steadily becomes liquid water where the hydrogen bonds are disrupted but still have a minor hold on the molecules in the liquid state.

Notice how between A-B no temperature change is recorded eventhough energy is added. During this stage energy is used to disrupt hydrogen bonds and is not used to increase the average kinetic energy of the molecules which will result in temperature change.

At point B the entire sample of water is in the liquid state
Between B-C water molecules are free to move. Heat energy is now absorbed and transformed into kinetic energy. The average speed of the molecules slowly increases and results in a temperature increase.
At point C there is enough energy for some of the particles to completely break away from the other molecules and enter the gaseous state.
Between C-D the liquid steadily becomes a gas.
At point D all the water sample is in the gaseous state.
Beyond point D gas particles absorb energy to further increase their average speed which results in a further temperature rise.