Melting and boling points are some of the physical properties of a certain substance that can be measured using a couple of instruments available in the laboratory.
The purpose of melting and boiling laboratory experiments is to measure the purity of a certain substance. It can also be used to identify a certain unknown compound by comparing it with with a set of known melting point values.
case 1. You know that water boils at approximately 100 degrees celsius at atmospheric pressure (room condition). If your water sample boils at 103 degrees celsius you probably have an impure water sample. Salts may have been added in your sample that causes the rise of the temperature.
case 2. You have a set of melting points of certain compounds:
o-toluic acid 103-105
Fluorene 114 -115
dl-Mandelic Acid 117-118
Benzoic Acid 121-122
Your unknown compound melts at about 132.4 degree celsius.
You can conclude that your unknown compound is more likely to be urea.
Hope this helps :)