A "parts book" is like a big book that has pictures and descriptions of all the different pieces and parts that go into making something. For example, imagine you have a toy car that you really like to play with. If something breaks on the car, you might need to get a new part to fix it. But how do you know what part to get? That's where a parts book comes in handy.
Inside the book, there will be different sections for each part of the car. You can look through the book and find the section for the part that's broken, like the wheels or the engine. Each section will have pictures of all the different options for that part, so you can see what they look like and make sure you're getting the right one.
The book will also have descriptions of each part, like its size and what it's made of. This can help you make sure that the part you're getting will fit and work correctly in your car.
So basically, a parts book is like a big guide that helps you find and choose the right pieces and parts to fix something when it breaks. It's like a "map" for repairing things!