What are good books about financial markets?
The classic undergraduate textbook is Financial Markets and Institutions from Mishkin and Eakins. I can wholeheartedly recommend this textbook check some local secondhand textbook stores where you can get it cheap (new book is unnecessarily pricey).

If you are not looking for a textbook I would recommend Ascent of Money by Ferguson- that’s mostly about history and it’s written in extremely simple language targeted at general audiences