Here's how it works:
* Interesting is an adjective, describing something that is engaging or captivating.
* Interest is a noun that can refer to:
* A feeling of wanting to know more about something. "I have a strong interest in history."
* Something that is engaging or captivating. "The book was a good read, full of interest."
* A share or stake in something. "He owns a 10% interest in the company."