the words "interested" and "interesting" are in the same word group as they are based in the noun "interest". however, their meanings are very different.
"interesting" is an active adjective, meaning that it causes interest.
"interested" is a passive adjective, meaning that it has interest for something.
a clear example can be "i am interested in this book, the book is really interesting."
generally speaking, an active adjective can end in -ing, and those will be adjectives causing a reaction or emotion. other examples of active adjectives are: boring, exciting, annoying, exhausting.
a passive adjective may end in -ed, and those will be describing the noun that is receiving the action. other examples of passive adjectives are: bored, excited, annoyed, exhausted.