I want to know the difference of meaning between 'stop'and 'prevent'.
The definition of stop (Oxford Dictionnary) is
(Of an event, action, or process) come to an end; cease to happen
The definition of prevent (Oxford Dictionnary) is
Keep (something) from happening
So the difference between the two is the moment you act. If the action has already started, you stop it. Otherwise you prevent it.