As the title says, the book explains how plants work! It takes a different approach from most books in that it doesn't really look at each plant part individually (e.g. leaves, stems, roots). Instead each chapter focuses on a specific plant system or behavior, which often requires multiple plant parts in order to function.
I enjoyed the book and learnt a fair bit, but as someone with no background in biology (not even high-school level stuff), some of the science jargon felt like it served to confuse me more than it did any good.
The book is trying to straddle a really really difficult line of being accessible enough while still being solidly rooted in proper scientific understanding. That's something I can really appreciate as a scientist myself, but somehow it didn't feel like it entirely hit the mark.
As a budding (eyoooo) gardener, while I ended up understanding a fair few new things, I do wish that the theory was eventually used to inform specific gardening practices. As it stands, the book mostly sticks to dispelling some common myths, but never really tells you how to garden properly - it's probably outside of its scope, but I do really wish it wasn't :)
The passable writing also has some slightly overly gendered overtones for my personal enby sensitivities, but nothing too egregious.
I'd recommend this for you if you know some basic biology of how cells work and are looking to nerd out by more deeply understanding plant behavior :)