^ I didn't mean to sound mean, I hope you didn't take it the wrong way.
The differences are not something we really can tell you in 1 posting, it takes time for anyone to learn them. What I recommend is to look closely at pictures of an authentic item and compare the details to the listing that you are interested in.
There are so many fakes out there. If you are trying to buy an authentic MJ item (especially commonly faked styles like Stam, Elise, Blake, Venetia, Stella, etc), please get it authenticated first before proceeding. You can also search for pictures of the real items, spend some time looking/studying the details. You will become familiar and be able to distinguish a good from bad item.