Melting point of a solid is defined as the temperature at which a solid changes into liquid. Melting point of a solid indicates the strength of the force of attraction between the particles of the solid. On heating a solid, its molecule absorbs energy in the form of heat and their kinetic energy increases. As the kinetic energy increase the temperature of the solid increases. As a result, the force of attraction between the molecules decreases and the molecules become more and more separated. This increases the potential energy of the molecule and the particles leave their fixed positions and start moving more freely. At a particular temperature, the separation of the molecules increases by a large amount and the solid melts and converts into liquid. This particular temperature is the melting point of that solid.
This video explains how to determine the melting point of ice.