Question

explain how the third law of motion applies to the rockets?

Answer 1

The action force is the jet of hot gases forced from the tail of the rocket. The jet of hot gases applies a force to the rocket that propels the rocket forward; this is the reaction force. The forces are internal to the system of rocket. Looking at the momentum involved, the hot gases gain momentum in the backward direction and the rocket gains an equal amount of momentum in the forward direction.
The equation of motion of a rocket can be deduced from the momentum principle.

Answer 2

Something like this ?