This book helps you understand calculus. Rather it probably helps you understand why you don’t already know calculus. Ouellette has an approachable likeable tone and uses a lot of interesting contemporary examples to help you understand things like derivatives and integrals and why you might care to even know this stuff. She delves into a lot of interesting math history and really works hard to make examples that are real-world and relevant, using such locations as Disneyland, a surfing beach in Hawaii and Las Vegas.
That said, I still don’t know calculus and I think it’s not her fault. The book, while upbeat and “you can do it” in tone is also sort of a popular approach to the work and so is sometimes jokey when maybe it should be more explanatory. Ouellette’s husband is a physicist and she admits herself that she was not the most eager of math students herself. So there’s a camraderie aspect that didn’t resonate with me [probably because I am a grouch] and every time they went to a new fancy location to illustrate some principle or another, I’d jadedly think “Oh I guess that vacation is a tax writeoff then.” Most people who are not grouches will enjoy this book.