could you plz help me that where should I use "might" and at what situation I should use "may" ??

my brother there is no difference between might and may just difference is that (may) is used for polit request for example may I come in or may I seat here. and might is used for 30% possibility I mean possibility but 30% for example it might rain to day. it mean it is not sure I mean its not comferm thanks. and you can ask questions from me