throw:the throw keyword is used to throw the exception manually that is when you feel a particular line in your code when executed is capable of having some exception then you use throw keyword as:

throw new MyException(arguments if any); this leads to instantiating of the MyException class and exception is thrown

throws: this is to be used when you are not using the try catch statement in your code but you know that this particular class is capable of throwing so and so exception(only checked exceptions).in this you do not use try catch block but write using the throw clause at appropriate point in you code and the exception is thrown to caller of the method and is handeled by it.