'Interested' : It is in past participle form. (Used as an adjective) It tells you how someone feels e.g. I am very interested in this book ... ESTOY muy interesado en este libro. 'Interesting' : It is in present participle form. It describes the things or people who cause the feeling of being interested. e.g. This book is very interesting for me ... ESTE LIBRO es muy interesante para mí. For the same reason, Only a living thing (or any object described as a living thing, e.g in a story) can be INTERESTED :D whereas anything, living or non-living can invoekt he feelings of being interested and thereby can be INTERESTING.

You can say this story is very interesting, but you can not say it is very interested, becaue you need to add a preposition after interested. For example, I am interested in the American history. Hope that can help you.