In order to understand divide the graph into parts and apply the key to the left in the first picture. The orange boxes represent the state of matter whether it be solid, gas, or liquid. The green are your x and y variables and in this case as heat energy increases so does temperature, the red is the process in which the state of matter takes to transform into another state of matter, meaning that as something is heated or cooled with enough energy it’s state of matter will change, as shown on the graph the red represents matter changing from heat energy (heating) and the blue shows lack of heat energy (freezing).