How can you explain the nature of the existence of the electrical resistance of a conductor?

Current is the movement of charged particles along a conductor. As they move, free electrons collide with positive ions, atoms and molecules of the substance from which the conductor is made. In a collision, electrons give up part of their energy to them, and part of the energy is dissipated in the form of heat (the conductor heats up).
Thus, when moving along a conductor, electrons experience resistance, which is called electrical. If the resistance of the conductor is small, then it heats up very little, if it is large, the conductor can get hot.