When you blog, you provide people with information for free. One way to expand on the information you give people and make money doing it is to write an e-book and sell it on your blog.
Ideally, your e-book will connect with the content on your blog and expand on it in some way. People won’t want to pay money for content you’ve previously given away.
For example, if you have a cooking blog, your e-book could be a short cookbook featuring previously unpublished recipes.
The recipes could have been tested by a group of people before publishing and not available anywhere else.