How does a resistor convert electricity into heat?

Hint : A resistor is defined as a passive two-terminal electrical component and implements electrical resistance as a circuit element. The resistors are used to reduce the current flow, to adjust the signal levels, to divide the voltages and, also to bias the active elements.

Complete Step by step answer:
The main function of the resistor is to limit the flow of the electric current. Thus, when a current flows through the resistor, the electrical energy is converted into heat energy. Hence the heat that is generated in the components of the circuit possesses some resistance and is dissipated into the air around the components.
The process in which the electrical energy is converted to heat energy is called Electric heating and the heating element inside every electric heater is the resistor. It works on the principle of Joule heating and, thus an electric current passing through the resistor will convert the electricity into heat energy.
The resistors affect both the current and the voltage. Thus, the voltage across each resistance will vary directly in proportion to the current that is flowing in it.
In general, the inelastic collisions of electrons that are moving through the conductor are the main cause of the resistance. The crystal structure of the metal atoms in the conductor hinders the flow of the electrons through it and this heat dissipation is called Joule heating which is the main source of the power dissipation in the resistor.

Note:
1. The resistor is measured in ohms.
2. The higher resistance implies more heat and, thus the higher the current, the larger the amount of heat generated.